A multinuclear NMR study of [Pt0(PPh3)2(alkene)] compounds containing asymmetric olefins.

Abstract The 1 H, 13 C, 31 P, and 195 Pt NMR spectra of [Pt 0 (PPh 3 ) 2 (η 2 -ABC(1)=C(2)XY)] compounds (ABC(1)=C(2)XY ( 1 ) A=B=X=Y=H; ( 3 ) A=B=X=H, Y=CN; ( 4 ) A=H, B= p -NO 2 -Ph, X=COOCH 3 , Y=CN; ( 5 ) A=H, B=Ph, X=COOCH 3 , Y=CN; ( 6 ) A=H, B=Ph, X=Y=CN; ( 7 ) A=H, B=OEt, X=Y=CN), where X and Y are electronacceptor substituents, and the 1 H spectrum of [Pt 0 (PPh 3 ) 2 (η 2 -C 60 )] ( 2 ) are reported together with extended analyses and assignments, based also on the ring current effect of the olefin phenyl in ( 4–6 ). Deviations from first order in the 13 C spectra allowed the determination of the relative signs of the coupling constants J(P(1), C) and J(P(2), C) of the alkene and of the triphenylphosphine carbons. Best fit simulation of the phosphine C ipso spectrum provided also the 13 C isotopic shift on phosphorus for ( 1 ). These compounds are characterised by strong differences between the two platinum–phosphorus coupling constants in the case of asymmetric olefins ( 3-7 ). The chemical shifts of alkene C(1) and C(2) indicate notable polarisation of the olefin after complexation, while the 1 J(Pt, C(1)) and 1 J(Pt, C(2)) values are in agreement with a stronger interaction of Pt with C(1) than with C(2). These findings together with the trend of 195 Pt chemical shifts confirm the important role played by back-donation in the bonding of platinum(0)–olefin compounds.