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Abstract

We have studied the ligand properties of cis-Ph₂PCH=CHPPh₂ at nickel(0). Several homoleptic nickel(0) alkene complexes react with the twofold molecular quantity of cis-Ph₂PCH=CHPPh₂ to afford the red crystalline homoleptic 1:2 complex Ni(cis-Ph₂PCH=CHPPh₂)₂ (1).The reactions of Ni(cdt) or Ni(C₂H₄)₃ with equimolar amounts of cis-Ph₂PCH=CHPPh₂ yield orange-yellow crystals of the homoleptic 1:1 complex {(µ-cis-Ph₂PCH=CHPPh₂)Ni}_n (2). Sparingly soluble 2 is presumably oligomeric with the (PCH=CHP)Ni moiety π-bonded to another nickel(0) center. The π bridges are rather stable and are only cleaved by strong π acceptors. For example, 2 reacts with CO to yield the known carbonyl complex (cis-Ph₂PCH=CHPPh₂)Ni(CO)₂ (3). In contrast to the above synthesis of 2, the 1:1 reaction of Ni(cod), with cis-Ph₂PCH=CHPPh₂ affords orange-red crystals of the alkene complex (cis-Ph₂PCH=CHPPh₂)Ni(cod)•THF (4) in moderate yield. Ni(1,5-hexadiene), reacts readily with cis-Ph₂PCH=CHPPh, (1:1) to give yellow (cis-Ph₂PCH=CHPPh₂)Ni(rac-η²,η²-C₆H₁₀) (5, 77%), which exhibits a fluxional diene coordination. That these thermally labile alkene complexes are formed at all, is ascribed to the chelate effect of the dienes. From the reaction of 2, 4 or 5 with ethyne, yellow microcrystals of (cis-Ph₂PCH=CHPPh₂)Ni(C₂H₂)•Et₂O (6) are obtained.