Nickel(0) and palladium(0) complexes with (Z,Z)-Ph2PCH2C(t-Bu)=N-N=C(t-Bu)CH2PPh2. Alkyne-to-alkenyl conversion in [Pd(MeOCOC CCOOMe){(Z,Z)-Ph2PCH2C(t-Bu)=N-N=C(t-Bu)CH2PPh2}]

Novel zero-valent metal complexes [ML2{(Z,Z)-Ph2PCH2C (t-Bu)=N-N=C(t-Bu)CH2 PPh2)] (M = Ni, L = CO, t-BuNC) with the azine diphosphine chelating in a n ine-membered ring were prepared. The nickel dicarbonyl complex was found to be in an equilibrium with its isomer containing (E,Z)-chelated azine dipho sphine, the equilibrium being on the side of the (Z,Z)-isomer below 60 degr ees C. A similar palladium complex (M = Pd, L-2 = CH3OCOC=CCOOCH3) prepared earlier was found to undergo a rearrangement with simultaneous alkyne-to-a lkenyl conversion of the acetylenedicarboxylate dimethyl ester ligand.