Synthesis of Di-tert-butyl(cyclopropyImethyI)phosphine, _______trans-PtCI₂(P(t-Bu)₂CH₂CHCH₂CH₂)₂, and PtCI(P(t-Bu)₂ CH=C(CH₃)CH₂)(P(t-Bu)₂CH₂CHCH₂CH₂). The Intramolecular Activation of C-C and C-H Bonds of a Cyclopropyl Phosphine

The synthesis of the cyclopropyl phosphine (t-Bu)₂PCH₂CHCH₂CH₂ (1) is described. When this new phosphine is combined with dichlorobis(benzonitrile)platinum(II) in toluene, the resulting product is trans-PtCl2(P(t-Bu)₂CH₂CHCH₂CH₂)₂ (2). In refluxing 2-methoxyethanol, compound 2 undergoes an intramolecular cyclometalation reaction in which both a C-C and a C-H bond of one of the cyclopropane rings are cleaved to form the chelating (σ-allyl complex PtCl(P(t-Bu)₂CH=C(CH₃)CH₂)(P(t- Bu)₂CH₂CHCH₂CH₂) (3). Complex 3 crystallizes in the monoclinic space group C⁵_2h,P2₁/c, with four formula units in a cell of dimensions a = 11.847 (5) A, b = 15.451 (7) A, c = 16.802 (8) Å, β = 116.70 (2), and V = 2747 A³. The final agreement indices for 4630 reflections having F₀² > 3σ(F₀²) are R(F) = 0.044 and R_W(F) = 0.047 (253 variables). Bond lengths in the five-atom chelate ring PtPC=CC are PtP = 2.279 (2) A, PC = 1.824 (8) A, C=C = 1.386 (11) Å, CC = 1.432 (10) A, and CPt = 2.018 (6) Å. Possible mechanims for the formation of 3 involve either initial C-H or C-C bond activation of the cyclopropane ring.