CC SiMe3 Research Articles

Coupling of acetylene molecules on ruthenium clusters, involving cleavage of C–Si bonds in the alkyne and coordination of a phenyl ring of a SiPh3 group

The reaction of [Ru3(CO)12] with the disubstituted acetylene Me3SiC≡CSiMe3 yields several compounds where cleavage of the C-Si bond has occurred thus allowing an easy coupling of carbon fragments to produce allene complexes [Ru4(CO)12(μ4-η(3)-Me3SiCCCSiMe3)] (2), differently substituted metallacycle compounds [Ru3(μ2-CO)2(CO)6{μ3-C(R)C(SiMe3)C(R')C(SiMe3)}] (3) [R = SiMe3, R' = CH3 (3a); R = H, R' = CH3 (3b); R = C≡CSiMe3; R' = H (3c)] and a pentanuclear ruthenium cluster containing three separate alkyne units; two with one SiMe3 substituent and one with two SiMe3 substituents, coordinated to the metal framework [Ru5(CO)12{μ3-(C2SiMe3)2}μ2-C2(SiMe3)2] (4). Another product of the reaction is the acetylide derivative [(μ-H)Ru3(CO)9(CCSiMe3)] (1a). In order to determine if this was an intermediate for the formation of the products already mentioned, the reaction of this compound was carried out with the two terminal alkynes HCCSiMe3 and HCCSiPh3. In the case of the reaction with the SiMe3 derivative, products included the same metallocyclopentadiene derivatives as well as the pentanuclear cluster already mentioned. If the acetylene is the SiPh3 derivative, products show coupling of SiPh3CC units with CCSiMe3 fragments and CO molecules, coordinated to mononuclear [Ru(CO)2(CCSiPh3){η(5)-(CCSiPh3)2C(OH)}] (7), dinuclear [Ru2(CO)3{Ph3Si(H)CC(H)CC(SiMe3)C(O)C(SiPh3)C(H)}] (8) and trinuclear [Ru3(CO)4{(Ph3Si(H)CC(H)CC(SiMe3)}{(H)CC(SiPh3)C(O)}] (9) clusters. One important characteristic in compounds 8 and 9 is that one of the phenyl rings of the SiPh3 substituent is η(6) coordinated to a ruthenium atom. Compounds 2 to 4(a-c) and 7 to 9 were characterized spectroscopically and by X-ray diffraction.

Boratatrozircenes: cycloheptatrienyl zirconium boratabenzene sandwich complexes – evaluation of potential η6–η5 hapticity interconversions

The salt metathesis reactions of [(η7-C7H7)ZrCl(tmeda)] (1) with various boratabenzene ligands Li(C5H5B–R) (R = H, CH3, CC–SiMe3) afford the 16-electron sandwich complexes [(η7-C7H7)Zr(η6-C5H5B–R)] (2: R = H, 3: R = CH3, 4: R = CC–SiMe3). The molecular structures of 3 and 4 were determined by X-ray diffraction analyses; they display distorted η6-coordinated boratabenzene ligands with short Zr–B bonds of 2.683(2) and 2.649(6) Å. The possibility of an η6–η5 hapticity interconversion, accompanied by B–L bond formation, upon addition of a Lewis base L (L = PMe3, 4-(dimethylamino)-pyridine) to 3 was studied. However, Zr–L bond formation was observed instead, leading to [(η7-C7H7)Zr(η6-C5H5B–CH3)(L)] (5: L = PMe3, 6: L = 4-(dimethylamino)-pyridine), even if a large excess of L was used.

Synthetic and computational studies of the palladium(iv) system Pd(alkyl)(aryl)(alkynyl)(bidentate)(triflate) exhibiting selectivity in C–C reductive elimination

Synthetic routes to methyl(aryl)alkynylpalladium(IV) motifs are presented, together with studies of selectivity in carbon-carbon coupling by reductive elimination from Pd(IV) centres. The iodonium reagents IPh(C≡CR)(OTf) (R = SiMe(3), Bu(t), OTf = O(3)SCF(3)) oxidise Pd(II)Me(p-Tol)(L(2)) (1-3) [L(2) = 1,2-bis(dimethylphosphino)ethane (dmpe) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3)] in acetone-d(6) or toluene-d(9) at -80 °C to form complexes Pd(IV)(OTf)Me(p-Tol)(C≡CR)(L(2)) [R = SiMe(3), L(2) = dmpe (4), bpy (5), phen (6); R = Bu(t), L(2) = dmpe (7), bpy (8), phen (9)] which reductively eliminate predominantly (>90%) p-Tol-C≡CR above ~-50 °C. NMR spectra show that isomeric mixtures are present for the Pd(IV) complexes: three for dmpe complexes (4, 7), and two for bpy and phen complexes (5, 6, 8, 9), with reversible reduction in the number of isomers to two occurring between -80 °C and -60 °C observed for the dmpe complex 4 in toluene-d(8). Kinetic data for reductive elimination from Pd(IV)(OTf)Me(p-Tol)(C≡CSiMe(3))(dmpe) (4) yield similar activation parameters in acetone-d(6) (66 ± 2 kJ mol(-1), ΔH(‡) 64 ± 2 kJ mol(-1), ΔS(‡)-67 ± 2 J K(-1) mol(-1)) and toluene-d(8) (E(a) 68 ± 3 kJ mol(-1), ΔH(‡) 66 ± 3 kJ mol(-1), ΔS(‡)-74 ± 3 J K(-1) mol(-1)). The reaction rate in acetone-d(6) is unaffected by addition of sodium triflate, indicative of reductive elimination without prior dissociation of triflate. DFT computational studies at the B97-D level show that the energy difference between the three isomers of 4 is small (12.6 kJ mol(-1)), and is similar to the energy difference encompassing the six potential transition state structures from these isomers leading to three feasible C-C coupling products (13.0 kJ mol(-1)). The calculations are supportive of reductive elimination occurring directly from two of the three NMR observed isomers of 4, involving lower activation energies to form p-TolC≡CSiMe(3) and earlier transition states than for other products, and involving coupling of carbon atoms with higher s character of σ-bonds (sp(2) for p-Tol, sp for C≡C-SiMe(3)) to form the product with the strongest C-C bond energy of the potential coupling products. Reductive elimination occurs predominantly from the isomer with Me(3)SiC≡C trans to OTf. Crystal structure analyses are presented for Pd(II)Me(p-Tol)(dmpe) (1), Pd(II)Me(p-Tol)(bpy) (2), and the acetonyl complex Pd(II)Me(CH(2)COMe)(bpy) (11).

Trans Bis-N-heterocyclic carbene bis-acetylide palladium(II) complexes

A series of square planar trans bis-N-heterocyclic carbene palladium(II) bis(acetylide) complexes of the type [(iPr2-bimy)2Pd(CC–R)2] (bimy = benzimidazolin-2-ylidene) (R = C6H5, C6H4F, C6H4OMe, SiMe3, C4H3S, C5H4N, C6H4CCC6H5 and 1-pyrene) were prepared by the addition of the corresponding lithium acetylides to the starting (iPr2-bimy)2PdBr2 complex in good to modest yields. The molecular structures of (iPr2-bimy)2Pd(CC–C6H5)2 (1) and [(iPr2-bimy)2Pd(CC–SiMe3)2] (4) were determined by single-crystal X-ray diffraction studies. UV/vis absorption studies reveal significant spectral changes depending on the nature of the acetylide ligands bound to the palladium center.

Structural characterisation of a series of acetylide-functionalised oligopyridines and the synthesis, characterisation and optical spectroscopy of platinum di-ynes and poly-ynes containing oligopyridyl linker groups in the backbone

A series of trimethylsilyl-protected bis(ethynyl)oligopyridine derivatives Me3SiCC–R–CC–SiMe3 (R = 2,2′-bipyridine-5,5′-diyl (1a), 2,2′-bipyridine-6,6′-diyl (2a), 2,2′:6′,2″-terpyridine-6,6″-diyl (3a), 4′-phenyl-2,2′:6′,2″-terpyridine-6,6″-diyl (4a)) has been synthesised and 2a–4a have been characterised by single crystal X-ray crystallography. The corresponding terminal di-ynes H–CC–R–CCH (1b–4b) and their dinuclear platinum(II) complexes trans-[(Et3P)2(Ph)Pt–CC–R–CC–Pt(Ph)(Et3P)2] (1M–4M) have been characterised spectroscopically and by single-crystal X-ray crystallography for 2M. Novel platinum(II) poly-yne polymers trans-[Pt(PBun3)2–CC–R–CC–]n (1P–4P) containing the oligopyridyl linker groups in the backbone have been synthesised by the CuI-catalysed dehydrohalogenation polycondensation reaction of 1b–4b and trans-[(Bu3P)2PtCl2] in Pri2NH–CH2Cl2. The polymeric materials exhibit decreasing thermal stability with increasing number of pyridine units in the linker group. In the absorption and phosphorescence spectra, the platinum(II) poly-yne and di-yne complexes 1P, 1M show red shifts whereas the complexes 2P–3P, 2M–3M show blue shifts of the S1 and T1 states. At room temperature, the phosphoresence spectra indicate some excimer formation whereas at 10 K, only intra-chain emission occurs. The results of the photophysical studies are compared with those obtained for other platinum(II)-containing poly-ynes and related organometallic polymers.

A new binuclear ruthenium complex with an annelated C7 bridge via an unprecedented [2 + 2] coupling reaction

Treatment of [Cl(dppe)2Ru–CC–CC–SiMe3 ] with [Fe(C5H5)2]PF6 leads to an unprecedented metal-assisted [2 + 2] coupling reaction on CγCδ bonds to obtain [Cl(dppe)2Ru–CC–CCHC(CH2 )CCRu(dppe)2Cl]PF6 with the charge highly delocalized over seven carbon atoms and including a cyclobutenyl bridge; the crystal structure was solved.

1,6-Bis(trimethylsilyl)hexa-1,3,5-triyne as a precursor to ruthenium clusters containing highly ethynylated ligands

The reaction of 1,6-bis(trimethylsilyl)hexa-1,3,5-triyne ( 1) with Ru 3(CO) 12 results in the formation of the butterfly cluster Ru 4(CO) 12( μ 4- η 1, η 1, η 2, η 2-Me 3SiCCC 2CCSiMe 3) ( 2) and the yellow binuclear complex Ru 2(CO) 6{ μ- η 2- η 4-C(CCSiMe 3)C(CCSiMe 3)C(CCSiMe 3)C(CCSiMe 3)} ( 3). Both complexes contain pendant ethynyl ligands that are potential sites for further reactivity. In the case of reaction of 1 with the tetranuclear cluster Ru 4( μ 4-PPh)(CO) 13 ( 4), the open chain molecule Ru 4(CO) 8( μ 3-PPh)[ μ 4 -η 2, η 4, η 2, η 4-(Me 3SiCC)CC(CCSiMe 3)C(CCSiMe 3)C-CC(SiMe 3)C(CCSiMe 3)C(CCSiMe 3)] ( 6) is formed, in which the co-ordination of a pendant ethynyl moiety has been realised.

Synthesis of condensed bicyclic thiophene derivatives from diyne systems

Metallation of the acetylenes MeCCR (R = CC–SiMe3, CCMe, CC–Sme, CC–Nalkyl2, S–CCSiMe3, S–CC–Me) with BuLi·ButOK, followed by the successive addition of carbon disulphide, t-butyl alcohol, and hexamethylphosphoric triamide gives thieno[2,3,-b]thiophene, thieno-1,4-dithi-ine, and some of their derivatives in reasonable yields.