SYNTHESIS, CHARACTERIZATION AND STRUCTURE OF SQUARE-PLANAR PALLADIUM(II) COMPLEXES WITH PHOSPHINE PYRIDINE HYBRID LIGANDS O-PH2PC6H4CH2O(CH2)NC5H4N-2 (N = 1-3) - ISOLATION OF THE 1ST TRANSITION-METAL COMPLEX WITH A TRANS-CHELATING BIDENTATE PN LIGAND

The reaction of Na2[PdCl4] or [PdCl2(PhCN)2] with an equimolar amount of new bidentate hybrid ligands having a P and a N donor atom capable of trans chelation, o-Ph2PC6H4CH2O(CH2)nC5H4N-2 (n = 1-3), gave mainly the 1:1 complex [PdCl2{o-Ph2PC6H4CH2O(CH2)nC5H4N-2}]. Depending on th e length of the backbone connecting the phosphino and the pyridyl grou ps, cis- or trans-co-ordinated complexes were mainly formed; when n = 1 the cis complex 1 was formed, but the ligands with longer bridges ga ve the trans complexes 2 and 3 respectively as the main products. From the reaction of the palladium(II) complex with o-Ph2PC6H4CH2O(CH2)nC5 H4N-2 (n = 2 or 3) the trinuclear complexes [Pd3Cl6{o-Ph2PCH4CH2O-(CH2 )nC5H4N-2}2] 4 (n = 2) and 5 (n = 3) were also obtained as minor produ cts and the cis-chelated complexes analogous to 1 could not be isolate d. The reaction of Na2[PdCl4] with 2 equivalents of o- Ph2PC4H4CH2O(CH 2)3C5HN-2 gave quantitatively the 1:2 complex trans-[PdCl2{o-Ph2PC6H4C H2O-(CH2)3C5H4N-2}2] 7 in which the ligand is bound only through the P atom. This complex is in equilibrium with the trans 1 : 1 complex 3 i n solution, dissociating one molecule of the ligand (K(eq) = 5.6 x 10( -3) mol dm-3, 35-degrees-C). On heating in CH2Cl2-tetrahydrofuran or d iethyl ether, 3 partially isomerised to the dinuclear complex [PdCl4{m u-o-Ph2PC6H4CH2O(CH2)3C5H4N-2}2] 6, in which the hybrid ligands act as bridges. The crystal structures of 1, 3 and 6 were determined; 3 is t he first example of a transition-metal complex with a trans-spanning c helate phosphine-pyridine hybrid ligand. The reaction of the ligand o- Ph2PC6H4CH2-O(CH2)3C5H4N-2 with K2[PtCl4], in contrast to the palladiu m complexes, always gave the 1:2 complex trans-[PtCl2{o-Ph2PC6H4CH2O(C H2)3C5H4N-2}2] 8 in good yield regardless of the ligand: Pt ratio. It did not dissociate in solution and the trans-chelated complex analogou s to 3 could not be isolated even from the reaction of K2[PtCl4] With an equimolar amount of the ligand o-Ph2PC6H4CHO(CH2)3C5H4N-2.