Reactions of allene, 2,3-dimethylbuta-1,3-diene, and buta-1,3-diene with bis(cyclo-octa-1,5-diene)-, bis(ethylene)(trimethylphosphine)-, and bis(ethylene)(tricyclohexylphosphine)-platinum; X-ray crystal structures of η-cyclo-octa-1,5-diene- and bis(trimethylphosphine)-(1,4-trans-divinylbutane-1,4-diyl)platinum

Abstract

Reaction of allene or buta-1,3-diene with [Pt(cod)₂](cod = cycle-octa-1,5-diene) gives (η-cycle-octa-1,5-diene)(2,3-dimethylenebutane-1,4-diyl)platinum (1) and (η-cycle-octa-1,5-diene)(1,4-trans-divinylbutane-1,4-diyl) platinum (2), respectively. The trans arrangement of the two vinyl groups in complex (2) has been con-firmed by an X-ray diffraction study [monoclinic, space group P2₁/n, Z=4, a= 9.082(6), b= 10.544(13), c= 15.293(17)Å, and β= 92.13(7)°], but crystal twinning limits refinement to R 0.111 (R′ 0.147). Displacement of co-ordinated cod from complex (2) with 2 mol equivalents of CNBu^t or PMe₃ affords [[graphic omitted]H-(CHCH₂)}L₂](L = CNBu^t or PMe₃). The structure of the trimethylphosphine complex has been identified by a single-crystal X-ray diffraction study. Crystals are triclinic space group Pa= 9.197(3), b= 11.283(4), c 9.555 (6)Åα= 87.10(4), β= 118.14(3), and γ= 98.89(3)°. Using 4 925 reflections collected at 213 K, refinement has converged at R 0.052 (R′ 0.0621). In contrast, treatment of (2) with 1 mol equivalent of PMe₃ gives (1 -σ,6–8-η-cis-2-trans-6-octadienediyl)(trimethylphosphine)platinum, which is also formed from [Pt(C₂H₄)₂-(PMe₃)] and excess of buta-1,3-diene. Reaction of [Pt(C₂H₄)₂{P(C₆H₁₁)₃}] affords the corresponding C₈ complex. 2,3-Dimethyl- and 2,3-diphenyl-buta-1,3-diene react with [Pt(cod)₂] to give (η-cycle-octa-1,5-diene)(2,3-dimethyl- and 2,3-diphenyl-but-2-ene-l,4-diyl)platinum respectively. The mechanistic implications of these observations are discussed.