The preparations of complexes of the type L2M(RC2R1) (where L = Ph,P, M = Ni, Pd, Pt, R = R' = CF,; L = Ph3P, M = Ni, Pt, R = R' = Ph, and R = Ph, R' = Me; L = Ph3P, M = Pd, Pt, R = R' = COOMe; and R = R' = CF3, M = Pd, Pt, L = n-Bu3P, Me2PhP) are described. From their nuclear magnetic resonance spectra these complexes appear to be approximately planar in solution.The vcGc observed in their infrared spectra indicate strong bonding of the acetylene to the metal.A new approach to the bonding in metal-acetylene complexes is proposed which can be extended to other n-complexes and which allows some predictions to be made.

The intermediates (RCOCH2CH-CH-CH2)-Fe(CO),+ AlC1,-(or PF,-) probably have the acyl oxygen co-ordinated to iron and lose protons stereoselectively to give syn-or anti-tricarbonyl-acylbutadieneiron depending on the base used. INTEREST in electrophilic substitution reactions of hydrocarbon ligands r-bonded to transition metals has centred on cyclic diene and dienyl complexes. An earlier report1 R1 R2 H Ac c Ac

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G12 SQQ)Summary The X-ray structural analysis of a substituted uncertainty exists over both the regio-and stereo-specificity tricarbonylallyliron cationic intermediate unambigu-of electrophilic attack on unsaturated ligands. I t has been ously demonstrates that tricarbonyl(trans, trans-hexa-2,k predicted' that the electron density in the .rr-orbital of a diene)iron undergoes stereospecific endo attack under complexed ligand will be greatest in the bonding region Friedel-Crafts conditions.

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