Structural studies on iminophosphine ligands and their palladium complexes

The crystal and molecular structures of the iminophosphine o-(Ph2P)C6H4CH=NC6H4OMe-4 (1) and its palladium complexes [Pd(eta(3)-C3H5){o-(Ph2P)C6H4CH=NC6H4OMe-p}]BF4 (2) and [Pd(eta(2)-fn){o-(Ph2P)C6H4CH=NC6H4OMe-4}] [fn = fumaronitrile, (3)] have been determined by X-ray analysis. In the free ligand (1), the planar imino group of E configuration is oriented, relative to the 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 the imino group rotation of 169.3 degrees and 145.3 degrees, respectively, around 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) involves 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 complexes, the chelate six-membered ring of the iminophosphine with palladium is not coplanar with the N-Pd-P coordination plane, the imino carbon atom and the 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 opposite 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 ethylenetetracarboxylate, (4)] are interpreted on the basis of a non-rigid conformation of the chelate iminophosphine, which undergoes a fast dynamic process whereby the N- and P-substituents move above and below the coordination plane.