OXIDATIVE LINEAR TRIMERIZATION OF ALKYNYL GROUPS IN (TRIMETHYLPHOSPHANE)NICKEL COMPLEXES - STRUCTURES AND THE ROLE OF LIGAND-RICH PRECURSORS NIX(C=CR)(PME(3))(N) (N=2-4)

Oxidative additions of 1-halogenoalkynes XC=CR to Ni(PMe(3))(4) afford high yields of pentacoordinate ionic alkynylnickel compounds [Ni(C=CR )(PMe(3))(4)](+)X(-) [R = SiMe(3), X = I (1); R = CMe(3), X = I (2), B r (3); R = SiEt(3), X = I (6), Br (7); R = SiiPr(3), X = I (10), Br (1 1), R = Ph, X = I (21), Br (22)] or complex molecules Ni(C=CR)X(PMe(3) )(3) [R = SiPh(3), X = I (14), Br (15); R = Ph, X = I (19), Br (20)]. Dissociation of trimethylphosphane gives square planar trans-Ni(C=CR)X (PMe(3))(2) [R = CMe(3), X = Br (4), Cl (5); R = SiEt(3), X = Br (8), Cl (9); R = SiiPr(3), X = Br (12), Cl (13); R = SiPh(3), X = I (16), B r (17), Cl (18); R = Ph, X = I (23), Br (24), Cl (25)] but with R = Si R(3)', X = I the title reaction dominates with formation of trans-Ni[C (C=CR)=CR(C=CR)]I(PMe(3))(2) [R = CMe(3) (26), SiEt(3) (29), SiiPr(3) (32)]. Thermal activation is necessary in order to obtain trans-Ni[C(C =CR)=CR(C=CR)]X(PMe(3))(2) [R = CMe(3), X = Br (27), Cl (28); R = SiEt (3), X = Br (30), Cl (31); R = SiiPr(3), X = Br (33), Cl (34)], while only thermal decomposition is observed with trans-Ni(C=CR)X(PMe(3))(2) (R = Ph, SiPh(3)). Examples for both types of reactivity including st ructural data are given: trans-Ni(C=CSiMe(3))Br(PMe(3))(2) and 25 crys tallize in the space group P $$($) over bar 1. Pentacoordinate 19 (spa ce group P2(1)) adopts a trigonal bipyramid of ligand donor atoms with equatorial phenylethynyl and iodo ligands.