Titanium σ-acetylides as building blocks for heterobimetallic transition metal complexes: synthesis and redox behaviour of π-conjugated organometallic systems

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Titanium σ-acetylides as building blocks for heterobimetallic transition metal complexes: synthesis and redox behaviour of π-conjugated organometallic systems
  Journal of Organometallic Chemistry 582 (1999) 126–138 Titanium   -acetylides as building blocks for heterobimetallic transitionmetal complexes: synthesis and redox behaviour of    -conjugatedorganometallic systems  Stephan Back  a,b , Robert A. Gossage  a , Gerd Rheinwald  b , Ignacio del Rı´o  a , Heinrich Lang  b, *,Gerard van Koten  a,1 a Debye Institute ,  Department of Metal  - Mediated Synthesis ,  Utrecht Uni   ersity ,  Padualaan  8  ,  NL - 3584   CH Utrecht ,  Netherlands b Technische Uni   ersita¨t Chemnitz ,  Institut fu¨r Chemie ,  Lehrstuhl Anorganische Chemie ,  Straße der Nationen  62  ,  D - 09111  Chemnitz ,  Germany Received 4 August 1998 Abstract A series of related Ti   -acetylides of the type {Ti}C   CR ({Ti} = (  5 -C 5 H 5 ) 2 Ti(CH 2 SiMe 3 );  2 : R = SiMe 3 ;  3 : R = C 6 H 3 (CH 2 NMe 2 ) 2 -3,5;  4 : R = C 6 H 2 I-4-(CH 2 NMe 2 ) 2 -3,5;  5 : R = C 6 H 4 CN-4;  6 : R = C 5 H 4 N-4;  7 : R = Fc, Fc = (  5 -C 5 H 4 )Fe(  5 -C 5 H 5 );  8 : R = C 6 H 4 (C   C{Ti})-4) have been prepared by reacting the corresponding lithium acetylides with {Ti}Cl ( 1 ). The X-raycrystal structure determination of {Ti}C   CSiMe 3  ( 2 ) is reported. This compound exhibits a one-dimensional (1D) arrangementwith respect to the Ti–C   C unit. The reaction of   2  with [CuCl] n  afforded  1  and [CuC   CSiMe 3 ] n  ( 10 ) and is proposed to occur viaprior formation of the dimeric intermediate [(  2 -{Ti}C   CSiMe 3 ) 2 Cu 2 Cl 2 ]. The chemical oxidation of {Ti}C   CFc,  7,  with Ag[BF 4 ]yielded HC   CFc and an undefined Ti species. Treatment of   5  or  6  with {Ru}N   N{Ru} ({Ru} = mer , trans -[RuCl 2 (NN  N)];NN  N =  3 -C 5 H 3 N(CH 2 NMe 2 ) 2 -2,6) produced intensively coloured heterodinuclear compounds, such as [{Ti}C   CC 5 H 4 N-4]{Ru}( 16 ). In contrast,  5  and  6  react with cationic Pt compounds of the type [{Pt}·L][X] ({Pt} = [Pt(C 6 H 3 {CH 2 NMe 2 } 2 -2,6] + ; L = H 2 O,MeCN; X = BF 4 , OTf) to give product mixtures rather than defined compounds. Electrochemical studies on some of the bimetalliccompounds show that the Ti(III) / Ti(IV) redox potential appears to be reversible and is shifted to a more negative value uponsubstitution of the Cl ligand in  1  by C   CR (compounds  2  –  8 ). Whereas the nature of R in {Ti}C   CR has an influence on theTi(III) / Ti(IV) redox potential, the attachment of a second metal onto the   -conjugated system has only negligible effect on theelectrochemical properties of the Ti centre. © 1998 Elsevier Science S.A. All rights reserved. Keywords :   Metallocenes; Alkynes; Metal–metal interaction; Conjugation; Cyclic voltammetry 1. Introduction Transition metal (TM) complexes in which metalcenters are linked by linear   -conjugated organic sys-tems (e.g.   -bonded alkynyl ligands) are currently stud-ied due to their potential as new materials which maypossess novel and / or interesting electronic properties[1]. These conjugated organic systems allow electronicinteraction or communication between attached metalcentres and can impose a one-dimensional (1D) direc-tionality. Such organometallic complexes resemble clas-sical organic non-linear optical (NLO) compounds, e.g.  para -nitroaniline [2], in which electron donor and ac-ceptor units are connected via a conjugated   -system[3]. The 1D organometallic complexes which are cur-rently used in NLO studies can be divided into threemain groups: (i) complexes containing a central lateTM complex fragment and one or two conjugated  Dedicated to Professor Alan Cowley on the occasion of his 65thbirthday.* Corresponding author. Fax:  + 49-371-5311833. 1 Also corresponding author. Fax:  + 31-30-252 3615. E  - mail addresses :   heinrich.lang@chemie.tu-chemnitz.de (H. Lang);g.vankoten@chem.uu.nl (G. van Koten)0022-328X / 99 / $ - see front matter © 1999 Elsevier Science S.A. All rights reserved.PII: S0022-328X(98)01068-7  S  .  Back et al  .  /   Journal of Organometallic Chemistry  582 (1999) 126–138  S  .  Back et al  .  /   Journal of Organometallic Chemistry  582 (1999) 126–138   127 electron donator / acceptor units bonded to it [4], (ii) twolate TM complex fragments linked by a   -conjugatedchain [5] and (iii) three or more late TM complexfragments incorporated into a   -conjugated system [6].However, only a few examples of heterobimetallic com-plexes have been reported in which an early (e.g. Ti, Zr,Hf) and a late TM unit are connected by a   -conju-gated organic system [7].This latter class of compounds is thought to have themost interesting electronic properties. One can assumethat an early TM complex fragment with the metalatom in a high oxidation state, e.g. titanocene deriva-tives containing a Ti(IV) metal centre, can function asan electron acceptor unit due to (energetically lowlying) vacant molecular orbitals [8]. A late TM complexfragment with the metal centre in a low oxidation state[e.g. Fe(II), Pt(II) or Ru(II)] could therefore act as anelectron donor unit. If both of these entities are con-nected via a conjugated   -system which supports elec-tronic communication, e.g. acetylide units, then thiscould result in changes in the two metal centres withrespect to their individual electronic behaviour. Previ-ously, it has been shown by cyclic voltammetric experi-ments that the electron density of a Ti(IV) centre intitanocene derivatives can be influenced by the acetylidesubstituents [9]. In order to ensure 1D directionality,one of the two reactive sites of the electron acceptingtitanocene fragment should be blocked and this leads tothe {Ti} unit [{Ti} = (  5 -C 5 H 5 ) 2 TiR; R = blocking an-ion]. This will permit the synthesis of titanocene mono-acetylides. The acetylenic units linked to Ti are of twotypes: the first class incorporates further potentiallyligating sites, such as 4-pyridyl or 4-benzonitrile groups.These sites can be used as linkage to a number of different late TMs, e.g. Pt(II) or Ru(II) containingfragments. The second class incorporates a late TMcomplex fragment directly, i.e. an organometallicacetylide. A third possibility for the build-up of multi-metallic systems is offered by the presence of a C   Ctriple bond of the acetylenic unit itself. Its coordinationchemistry to TM complexes, e.g. Cu(I), is well knownand a number of compounds, in which an acetylide is  2 -coordinated to a Cu(I) centre, has been reported[10]. This latter approach does not result in a 1D but a2D arrangement of the respective metal atoms and canalso be used to give some insight into the stability of the Ti acetylide   -bond. Moreover, this allows for thepossibility to influence an early–late TM interactiondirectly via coordination of the bridging C   C unit.These heterometallic compounds will allow the investi-gation of early–late TM interaction along organic   -conjugated fragments. Thus, an attempt is made to usesuch multimetallic molecules as molecular dipoles and / or model compounds for ‘nanoconducting’ materials. 2. Results and discussion 2  . 1 .  Synthesis of titanium mono - acetylides The titanocene monochloride {Ti}Cl ( 1 ) {{Ti} = (  5 -C 5 H 5 ) 2 Ti(CH 2 SiMe 3 )} is obtained in high yield by thereaction of titanocene dichloride with neosilyl magne-sium chloride [11]. This reaction serves as the basis forthe preparation of a series of titanocene mono-acetylides, which are virtually 1D with respect to theTi-acetylide unit. The synthesis of compounds  2  –  8  (Eq.1) was conducted following well-documented proce-dures for the build-up of titanocene bis(acetylides) [12].Compounds  2  –  6  and  8  were obtained as yellow toorange solids (60–80% yield) which are stable at 25°C if stored under a nitrogen atmosphere. Compound  7  ex-hibits an intensively purple colour. Analogous intensivecolours have been obtained for bis(alkynyl) titanocenescarrying ferrocenyl (Fc) as terminal group of theacetylide units [7]. The FAB mass spectroscopic investi-gation of the Ti acetylides  2  –  8  revealed a peak for themolecular ion [M] + at the expected  m / z  values inaddition to the expected fragmentation patterns.(1)The C   C stretching vibration in the IR spectrum is themost informative spectroscopic tool for monitoring theprogress of the reaction. While the corresponding freeacetylenes have a   C   C  vibration in the range of 2100and 2110 cm − 1 , compounds  3  –  8  exhibit   C   C  vibrationsaround 2070 cm − 1 (Table 1). In the IR spectrum of   2 ,this absorption appears at much lower frequency (2017cm − 1 ). These values resemble the data obtained forbis(alkynyl) titanocenes of the type (  5 -C 5 H 4 SiMe 3 ) 2 M(C   CR) 2  (M = Ti, Zr, Hf, e.g. R =  S  .  Back et al  .  /   Journal of Organometallic Chemistry  582 (1999) 126–138  S  .  Back et al  .  /   Journal of Organometallic Chemistry  582 (1999) 126–138  128Table 1Representative spectroscopic data (IR,  1 H and  13 C{ 1 H}-NMR) of the Ti acetylides  2  –  8  and {Ti}Cl ( 1 ) for comparisonIR a {Ti}C   CR  1 H-NMR b 13 C{ 1 H}-NMR c C 5 H  5  TiC H  2  C  5 H 5  Ti C  H 2 R =  Ti C    C TiC   C  {Ti}Cl  1  – 6.31 2.18 115.6 79.7 – – 2017SiMe 3  6.22 2  1.60 113.0 81.2 164.6 128.62069 6.27 1.64 112.9 3  81.0C 6 H 3 (CH 2 NMe 2 ) 2 -3,5 143.7 123.9 4 C 6 H 2 I-4-(CH 2 NMe 2 ) 2 -3,5 2069 6.27 1.64 112.9 81.0 143.7 123.8 5 C 6 H 4 CN-4 2078 6.29 1.75 113.1 83.8 148.8 122.22079 6.25 1.72 113.2 6  83.7C 5 H 4 N-4 148.9 121.0 7 Fc 2052 6.25 1.57 112.7 77.7 140.1 122.82076 6.27 1.65 112.9 81.5 140.1 8  124.3C 6 H 4 C   C{Ti}-4 a Recorded in KBr (cm − 1 ). b Relative to SiMe 4  (  = 0.00 ppm). c Relative to SiMe 4  (  = 0.00 ppm). Chemical shifts are reported in    units (ppm) downfield from SiMe 4  with the solvent as internal referencesignal. SiMe 3  [13], Ph [14], Fc [7]) and indicate likewise aweakening of the C   C bond upon binding to Ti [15,16].The comparison of the  1 H-NMR spectrum of   1  withthose of complexes  2  –  8  reveals that the signals of theprotons of the C 5 H 5  group appear at virtually the samefrequency, while those of the methylene protons of theneosilyl group are shifted by ca. 0.5 ppm to higher field(Table 1). The resonance signals of the protons of theother organic fragments were found in the expectedregions as sharp and well-resolved signals. In the 13 C{ 1 H}-NMR spectra of   2  –  8 , the resonance signals of the C 5 H 5  and  C  H 2 Si units are only slightly shifted tohigher field relative to those of the starting material  1 (Table 1). In general, by substitution of the Cl ligand in 1  by organic acetylides other than C   CFc, the respec-tive signal of Ti C  H 2 Si is shifted to lower field while the 13 C{ 1 H}-NMR spectrum of   7  shows this signal dis-placed slightly to higher field. The resonance signals of the acetylenic carbon atoms, which for free acetylenesare normally found between 80 and 100 ppm [17], arestrongly shifted to lower field. In the  13 C{ 1 H}-NMRspectra of complexes  2  –  8 , the respective signals forTi C    C are found between 140 and 165 ppm while thesignals for TiC   C   can be found around 125 ppm (Table1). Similar observations of strong shifts to lower field of these carbon signals were made for bis(alkynyl) ti-tanocene and alkynyl titanocene monochlorides. Inthese cases, the Ti centred acetylenic carbon atomsTi C     have been found to exhibit resonance signalsbetween 145 and 173 ppm [15]. This contrasts the shiftsof the resonance signals of, e.g. Ti = CR 2 , which werefound between 260 and 360 ppm [18]. Therefore, adouble bond character of the Ti acetylide   -bond canbe excluded.By cooling a pentane solution of {Ti}C   CSiMe 3  ( 2 )to  − 40°C, yellow crystals have been obtained whichwere suitable for a X-ray structural determination. Thesolid state structure of the prototypical Ti acetylide  2  isgiven in Fig. 1. Significant structural details are listed inTable 2. However, the earlier synthesised, analogoustitanocene complex (  5 -C 5 H 4 SiMe 3 ) 2 Ti(CH 2 SiMe 3 )-(C   CSiMe 3 ) was obtained as a yellow oil [19].Complex  2  crystallises in the monoclinic space group P 2 1 / n  with one independent molecule per unit cell. Acomparison of the data obtained for  2  to that of {Ti}Cl( 1 ) [11,20] reveals that the bond lengths and angles of the {Ti} fragment are virtually unchanged [20]. How-ever, the main structural features of   2  appear to com-bine the structural results obtained for alkynyl andalkyl titanocene derivatives. The Ti–C(sp) distance, i.e.Ti(1)–C(1) [2.120(4) A˚], as expected, is significantlyshorter than Ti–C(sp 3 ) bond lengths, e.g. in (  5 -C 5 H 5 ) 2 TiMe 2  [2.181(2) and 2.170(2) A˚] [21], (  5 -C 5 H 5 ) 2 Ti(CH 2 Ph) 2  [2.239(6) and 2.210(5) A˚] [22] or theone of Ti(1)–C(6) [2.166(4) A˚] in molecule  2 . It resem-bles rather separations found in, for example, themonoalkynyl titanocene [(Me 2 Si) 2 (  5 -C 5 H 2 SiMe 3 ) 2 ]-TiCl(C   CSiMe 3 ) [2.10(2) A˚] [19]. The C(1)–C(2) sepa-ration of 1.222(5) A˚resembles values of organic ororganometallic C   C distances [17]. The C(2)–Si(1) andC(6)–Si(2) bond lengths of 1.831(4) and 1.869(4) A˚, Fig. 1.  ORTEP  drawing (50% probability level) of   2  with moleculargeometry and atom numbering scheme.  S  .  Back et al  .  /   Journal of Organometallic Chemistry  582 (1999) 126–138  S  .  Back et al  .  /   Journal of Organometallic Chemistry  582 (1999) 126–138   129Table 2Selected bond lenghts (A˚) and angles (°) for  2 Si(1)–C(2)Ti(1)–C(1) 1.831(4)2.120(4)2.166(4)Ti(1)–C(6) Si(2)–C(6) 1.869(4)2.0793(7) C(1)–C(2)Ti(1)–D(1) a 1.222(5)Ti(1)–D(2) a 2.0749(7)C(1)–Ti(1)–C(2) C(1)–C(2)–Si(1)94.68(15) 167.2(4)Si(2)–C(6)–Ti(1)134.80(4) 129.2(2)D(1)–Ti(1)–D(2)C(2)–C(1)–Ti(1) 174.0(4) a D(1), D(2): centroids of the cyclopentadienyl ligands. In contrast, the monoalkynyl titanocene compound  2 lacks this chelating effect. Consequently, for  2  is ex-pected a coordinative behaviour that is comparable tothat of organic alkynes or metal acetylides [10a,27]. Amechanism of the complexation reaction of the mono-and bis(alkynyl) compounds  A  and  B  has been sug-gested earlier, in particular for the reaction of (  5 -C 5 H 4 SiMe 3 ) 2 Ti(CH 2 SiMe 3 )(C   CSiMe 3 ) with [CuCl] n [19]. The latter case showed that scrambling of the  -bonded groups occurred, leading finally to the forma-tion of stable [(  5 -C 5 H 4 SiMe 3 ) 2 Ti(C   CSiMe 3 ) 2 ]CuCl(cf.  B ), (  5 -C 5 H 4 SiMe 3 ) 2 Ti(CH 2 SiMe 3 )Cl and[CuCH 2 SiMe 3 ] 4 . In order to further study these reac-tions and to investigate the use of the C   C unit inmono-(alkynyl) Ti derivatives for the synthesis of het-erometallic molecules, compound  2  has been reactedwith either [CuCl] n  (1:1 molar ratio) or[Cu(NCMe) 4 ][BF 4 ] (2:1 molar ratio), respectively. TheseCu(I) salts have been chosen because of their well-known reactivity towards C   C triple bonds [12].(2)The reaction of   2  with [CuCl] n  in THF ( − 78°C) (Eq. 2)led to a colour change from orange to red after 10 min.The course of the reaction was monitored via IR spec-troscopy. With the red colour intensifying, the appear-ance of a band at 1920 cm − 1 (  C   C ) was detected whilethe band at 2018 cm − 1 (  C   C  of   2 ) lost intensity. Thisnew band is assigned to the absorption band arisingfrom   2 -coordination of the C   C fragment to Cu(I), i.e.to the formation of   9 . From literature reports, a num-ber of acetylene complexes with Cu 2 Cl 2  bridging unitsare known [12,28], inter alia, [{  2 -(  5 -C 5 H 5 )Fe(CO) 2 (C   CPh)} 2 Cu 2 Cl 2 ] [29a] or the [(CO) 5 Re]containing acetylides by Beck et al. [29b,c]. From thesame experiment on laboratory scale, again starting at − 78 °C, it appeared that on rising the temperature aprecipitate begins to appear which was graduallyformed, and subsequently identified as [CuC   CSiMe 3 ] n ( 10 ) [30]. After filtration of the reaction mixturethrough a pad of Celite,  1 H-NMR spectroscopy of thefiltrate showed that the Ti monochloride {Ti}Cl ( 1 ) hadbeen formed. From a second experiment conductedexclusively at  − 78°C, an orange solid could be iso-lated. The IR spectrum of this solid contained again anintensive absorption band at 1920 cm − 1 , together with  C   C  of   10 . As the  1 H-NMR spectrum of a solution of the yellow solid in THF- d  8  at  − 78°C revealed broadsinglets at virtually the same resonance frequencies asfor  2 , assignment of the resonance pattern was notrespectively, are typical values for carbon–silicon dis-tances in organic or organometallic compounds [23].The angle enclosed by the   -bound organic ligands[C(1)–Ti(1)–C(6) 94.68(15)°] is significantly smallerthan these angles found in, for example,bis(alkynyl)titanocenes (around 100°) [15] but resemblesvalues obtained for titanocene dichloride derivatives[24]. The angles C(2)–C(1)–Ti(1) [174.0(4)°] and C(1)– C(2)–Si(1) [167.2(4)°] exhibit a somewhat stronger devi-ation from linearity as compared with themonoacetylide complex [(Me 2 Si) 2 (  5 -C 5 H 2 SiMe 3 ) 2 ]-TiCl(C   CSiMe 3 ) [Ti–C–C: 176(1)°; C–C–Si: 174(1)°][19]. The angle Si(2)–C(6)–Ti(1) [129.2(2)°] is clearlyless deviated from the ideal tetrahedral angle as com-pared with this angle [136.9(1)°] in [(  5 -C 5 H 5 ) 2 TiCl(CH 2 SiMe 3 )] ( 1 ) [20]. This means that theincoming C   CSiMe 3  unit modifies the electronic systemof the {Ti} fragment in such a way that a proposedhyperconjugation in the TiCH 2 SiMe 3  fragment is lessfavoured [20].The solid state structure of   2  clearly shows that thedesired 1D array is present. Therefore, the formal sub-stitution of SiMe 3  by other ligands should give rise tosimilar linear arrangements. 2  . 2  .  Reactions of   { Ti  } C    CSiMe 3   (  2   )   with Cu (  I   )  compounds The coordination chemistry of mono- andbis(alkynyl) titanocene derivatives has been thoroughlyinvestigated and a number of stable mixed-metal com-pounds have been prepared, e.g. with Cu(I) compounds[12,15]. This led to the formation of heterobimetallicassemblies such as in compounds  A  [25] or  B  [26].  S  .  Back et al  .  /   Journal of Organometallic Chemistry  582 (1999) 126–138  S  .  Back et al  .  /   Journal of Organometallic Chemistry  582 (1999) 126–138  130Scheme 1. possible. However, a strong indication for the presenceof   9  was obtained from FAB MS investigations. Thespectra revealed peaks at  m / z  922 and 425 with thecorrect isotope patterns which can be assigned to themolecular ion peak of   9  and the fragmentation ion[({Ti}C   CSiMe 3 )Cu] + , respectively. Complex  9  is ther-mally unstable and decomposes rapidly in solution atelevated temperatures while in the solid state it can behandled for only short periods of time. Due to theinstability of   9 , a satisfactory elemental analysis couldnot be obtained.In contrast with the well-defined reaction of   2  with(CuCl) n , the reaction of   2  with[Cu(NCMe) 4 ][BF 4 ] inTHF ( − 78°C) led solely to the formation of an in-tractable mixture of reaction products. After evapora-tion of all volatile material and subsequent work-up atlow temperature, IR spectroscopy revealed the absenceof a band in the typical region of    CN  (2200–2300 cm − 1 )[32]. Furthermore, no evidence for   2 -coordination of the C   C bond to Cu(I) was obtained neither from IRnor from  1 H-NMR (CH 2 Cl 2 ,  − 78°C) spectra of theresulting yellow residue.These reactions of   2  with Cu(I) salts indicate that  2 -coordination of the C   C unit to Cu(I) occurs, butthat the resulting intermediates are prone to rapid ligandexchange reactions. These results corroborate the earlierresults for the reaction of [(  5 -C 5 H 4 SiMe 3 ) 2 Ti(CH 2 SiMe 3 )(C   CSiMe 3 )] with [CuCl] n [31]. However, in the case of [(  5 -C 5 H 5 ) 2 Ti(CH 2 SiMe 3 )(C   CSiMe 3 )],  2 , it is solely Ti– C(acetylide)   -bond cleavage that is observed. Theobvious difference with the reaction discussed above isthe absence of a SiMe 3  substituent on the cyclopentadi-enyl ligands in complex  2 .Apparently, also the anion is important, as in the caseof [CuCl] n  a selective formation of {Ti}Cl ( 1 ) and[CuC   CSiMe 3 ] n  ( 10 ) is observed. A comparable influ-ence of the anion on the exchange behaviour of thealkynyl groups between the Pt(II)–alkynyl compound{Pt}C   CSiMe 3  ({Pt} = [(  3 -NCN)Pt] + ; NCN = [C 6 H 3 (CH 2 NMe 2 ) 2 -2,6] − ) and Cu(I)-salts has been ob-served. The reaction of this mono-alkynyl metalcompound with [CuCl] n  led to the selective formation of {Pt}Cl and [CuC   CSiMe 3 ] n  ( 10 ) via prior formation of an intermediate with   2 -alkynyl-to-Cu(I) coordination[33]. 2  . 3  .  Redox stability of   { Ti  } C    CFc  (  7   )  Compound  7  is comprised of a molecule in which areducible group, {Ti}, and an oxidisable group, Fc(ferrocenyl), are connected via a unit which allowselectronic communication. Therefore, it was of interestto investigate how this arrangement would influence theredox behaviour of these two fragments. In general,reduction of titanocene derivatives is readily achieved bytheir reaction with activated Mg metal [34]. However,  7 remains unchanged in the presence of activated Mgmetal, even after prolonged stirring (THF, 25°C) andcan be recovered quantitatively from the reaction mix-ture. Thus, the reducing power of Mg is not sufficient toadd a single electron to the Ti(IV) centre of complex  7 .The change to a stronger reducing agent such as Na(THF, 0°C) led to the formation of a complex mixtureof products which could not be identified (IR, NMR).Similarly, reaction of   7  with Ag[BF 4 ] (THF, 0°C) in anattempt to oxidise the Fe(II) centre gave a mixture of products. Extraction of this mixture (pentane, THF)gave a pentane solution of HC   CFc ( 11 ) and a THFsolution containing a green compound, which could notidentified unequivocally. Thus, compound  7  is neitherstable to chemical reduction nor to oxidation [8]. 2  . 4  .  Reacti   ity of   5   and   6   towards late transition metal complexes Another strategy to obtain ‘early–late’ heterometalliccompounds is the reaction of suitable late TM com-plexes with the  N  -ligating site of compounds  5  or  6 .Therefore, these molecules were reacted with thecationic Pt complexes [{Pt}·H 2 O][BF 4 ] ( 12 ) and[{Pt}·NCMe][OTf] ( 13 , see Scheme 1) [35] as well as withthe neutral dinitrogen bridged Ru complex  14  [36]. Here,the Ti acetylide could act as an   1 -coordinated ligandafter displacement of H 2 O, MeCN or N 2 , respectively(Scheme 1).
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