Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 21. Reactivity of µ-(methoxy-p-tolylmethylene) and µ-(p-tolylmethylidyne) groups at a platinum–tungsten centre. X-Ray crystal structure of [PtW{µ-C(OMe)C6H4Me-4}(µ-Ph2PCH2PPh2)(CO)5]

Abstract

Treatment of [PtW{µ-C(OMe)R}(CO)₅(cod)](R = C₆H₄Me-4, cod = cyclo-octa-1,5-diene) with dppm (Ph₂PCH₂PPh₂) affords [PtW{µ-C(OMe)R}(µ-dppm)(CO)₅](1), the structure of which has been established by X-Ray crystallography. As expected, the platinum–tungsten bond [2.818(3)Å] is spanned by the dppm and C(OMe)R ligands. The five-membered ring involving the chelating phosphine and the two metal atoms adopts an envelope conformation with one of the P atoms lying out of the plane. The [graphic omitted] ring is asymmetric [Pt–C 1.97(3), W–C 2.49(3)Å]. The platinum atom carries one terminal carbonyl ligand and the tungsten atom four, making the co-ordination at these two metal centres essentially square planar and octahedral, respectively. Compound (1) reacts with HBF₄·OEt₂ to yield the salt [PtW(µ-CR)(µ-dppm)(CO)₅][BF₄], and with BBr₃ to give [PtWBr(µ-CR)(µ-dppm)(CO)₄], but the latter is better prepared by treating the salt with NEt₄Br. Reactions of the complex [PtW(µ-CR)(µ-dppm)(CO)₅][BF₄] with several nucleophilic reagents have been investigated leading to the synthesis of the compounds [PtW(µ-CRR′)(µ-dppm)(CO)₅](R′= Me, H, CCBu¹, or SC₆H₄Me-4) and [PtW{µ-C(η²-C₅H₅)R}(µ-dppm)(CO)₄]. The n.m.r. data (¹H, ³¹P-{¹H}, ¹³C-{¹H}, and ¹⁹⁵Pt-{¹H}) for the new compounds are reported and discussed.