Structural studies on iminophosphine ligands and their palladium complexes

The crystal and molecular structures of the iminophosphine o-(Ph2P)C6H4CH=N C6H4OMe-4 (1) and its palladium complexes [Pd(eta(3)-C3H5){o-(Ph2P)C6H4CH=N C6H4OMe-p}]BF4 (2) and [Pd(eta(2)-fn){o-(Ph2P)C6H4CH=NC6H4OMe-4}] [fn = fum aronitrile, (3)] have been determined by X-ray analysis. In the free ligand (1), the planar imino group of E configuration is oriented, relative to th e PPh2 unit, so that the CH=N hydrogen atom points towards phosphorus, with the nitrogen atom on the opposite side. In (2) and (3) the iminophosphine behaves as a P,N-chelate ligand, this coordination mode being achieved by t he imino group rotation of 169.3 degrees and 145.3 degrees, respectively, a round its bond with the ortho disubstituted phenyl ring. Complex (2) shows a structural disorder with two different orientations of the allyl ligand. The trigonal planar coordination around the central metal in complex (3) in volves the P- and N-donor atoms of (1) and the eta(2)-bound olefin, with a marked lengthening of the olefinic carbon-carbon bond. In both the complexe s, the chelate six-membered ring of the iminophosphine with palladium is no t coplanar with the N-Pd-P coordination plane, the imino carbon atom and th e ortho disubstituted phenyl group lying on the same side out of the N-Pd-P plane, whereas the N-substituent and one of the PPh2 groups are on the opp osite side. The H-1-n.m.r. spectra at low temperatures of (2) and (3), and of [Pd(eta(2)-tmetc){o-(Ph2P)C6H4CH=NCMe3}] [tmetc = tetramethyl ethylenete tracarboxylate, (4)] are interpreted on the basis of a non-rigid conformati on of the chelate iminophosphine, which undergoes a fast dynamic process wh ereby the N- and P-substituents move above and below the coordination plane .