Reductive dehalogenation of chloro(alkynyl)phosphines by octacarbonyldicobalt

Abstract

Reductive dehalogenation of the (chloro)(phenylethynyl)phosphine (2,4,6- tBu 3C 6H 2O)(PhCC)PCl, I, by Co 2(CO) 8, II, yields the neutral phosphenium ion complex [(R)(R′)]P=Co(CO) 3, III, (R = 2,4,6- tBu 3C 6H 2O; R′ = (η 2-C≡CPh)Co 2(CO) 6), which contains a trigonally planar coordinated phosphorus atom. When NaCo(CO) 4, V, is used instead of II a dinuclear complex, Co 2(CO) 6[μ 2-P(R)(R′)] 2, VI, (R = 2,4,6- tBu 3C 6H 2O; R′ = C≡CPh) is formed in which the phosphido ligands P(R)(R′), bridge in a μ 2 fashion two Co(CO) 3 units. The mechanism of formation of VI, involving a formal dimerization of two [(2,4,6- tBu 3C 6H 2O)(PhC≡C)]P=Co(CO) 3 fragments, is discussed. However, ( tBu)(PhC≡C)PCl, VII, reacts with II, to yield the cluster compound VIII, containing the two μ 2-bridging units ( tBu)[(η 2-C≡CPh)Co 2(CO) 5]P and ( tBu)(PhC≡C)P. Compounds II and VI–VIII were identified from their analytical and spectroscopic (IR, 1H-, 13C- and 31P-NMR) data. The molecular structure of the cluster compound VIII was determined by an X-ray diffraction study.