(R2PC2H4PR2)PD-0-1-ALKYNE COMPLEXES

Displacement of the ethene ligand in (d(i)ppe)Pd(C2H4)(d(i)ppe = (Pr2P C2H4PPr2)-Pr-i-Pr-i) by 1-alkynes RC = CH affords the mononuclear comp lexes (d(i)ppe)Pd(RC = CH) (R = Me (2a), Ph (3a), CO2 Me (4), SiMe3 (5 )). The molecular structure of 3a has been determined by X-ray crystal lography. Mononuclear 2a and 3a have been reacted with stoichiometric amounts of (d(i)ppe)Pd(eta(1).C3H5)(2) as a source for [(d(i)ppe)Pd-0] to yield the dinuclear derivatives {(d(i)ppe)Pd}(2)(mu.RC = CH)(R = M e (2b), Ph (3b)). By the reaction of (d(i)ppe)Pd(C2H4) with difunction al vinylacetylene the mononuclear complex (d(i)ppe)Pd{(1,2-eta(2))-RC = CH} (R = CH = CH2 (6a)) is formed, which is in equilibrium with isom eric (d(i)ppe)Pd{(3,4-eta(2))-H2C = CHC = CH} (6b). Addition of [(d(i) ppe)Pd-0] to 6a,b yields dinuclear {(d(i)ppe)Pd}(2)(mu-RC = CH) (R = C H = CH2 (6c)). Reaction of (d(i)ppe)Pd(C2H4) with butadiyne affords (d (i)ppe)Pd(eta(2)-HC = CC = CH (7c). From d(i)ppe, Pt(cod)(2), and C4H2 the Pt homologue has also been synthesized and thus, together with th e already known Ni derivative, the series (d(i)ppe)M(eta(2)-HC = CC CH (M = Ni (7a), Pd (7c), Pt (7f)) is now complete. When 7c and [(d(i)pp e)Pd-0] are combined, the dinuclear complex {(d(i)ppe)Pd}(2)(mu-RC = C H (R = C = CH) (7e)) is formed in solution, whereas isomeric {(d(i)ppe )Pd}(2){mu-(1,2-eta(2)):(3,4-eta(2))-HC = CC = CH} (7d) is present in the solid state. The preparation of the Pd-0-1-alkyne complexes refute s the conventional wisdom that this type of compound is inherently uns table. By reaction of (d(i)ppe)Pd(C2H4) with internal alkynes C2R2 the complexes (d(i)ppe)Pd(RC = CR) (R = Me (8a), Ph (9), CO2Me (10), SiMe 3 (11)) have also been prepared. Combining 8a with [(d(i)ppe)Pd-0] aff ords dinuclear {(d(i)ppe)Pd}(2)(mu-MeC = CMe)(8b). Finally, solution t hermolysis of 2b and 8b gives rise to dinuclear alkyne-free Pd-2(d(i)p pe)(2) (12).