SYNTHESIS, STRUCTURE AND REACTIVITY OF PT-II COMPLEXES CONTAINING THE[O-(DI-O-TOLYLPHOSPHINO)BENZYL] CYCLOMETALATED LIGAND TOWARDS ALPHA-STABILIZED PHOSPHORUS YLIDES

The reaction of [Pt(C <^> P)(NCMe)(2)]ClO4 2 [C <^> P = ortho -(di-ort ho-tolylphosphino)benzyl], with the alpha-stabilized phosphorus ylides Ph3P=C(H)R (R=COMe, COPh, COOMe, CN) in a 1:1 molar ratio results in the formation of [Pt(C <^> P){C(H)(R)PPh3}(NCMe)]ClO4 (R = COMe 3, COP h 4, COOMe 5. CN 6). Complexes 3-6 appear as single isomers in which t he ylide is selectively C-coordinated trans to the P atom of the C <^> P ligand. The displacement of the remaining coordinated NCMe ligand b y adding more ylide was only successfully accomplished with Ph3P=C(H)C N, giving [Pt(C<^>P){C(H)(CN)PPh3} (NC-C(H)PPh3)]ClO4 7, in which one ylide is C-coordinated trans to the P atom of the C <^> P ring and the other ylide is N-coordinated trans to the C atom, showing the ambiden tate character of Ph3P=C(H)CN as a ligand. The reaction of [Pt(C <^> P )(mu-Cl)](2) 1 with PPh3 (1:2 molar ratio, CH2Cl2, r.t.) results in th e formation of the two expected isomers trans- and cis-[Pt(C<^> P)Cl(P Ph3)] (8 and 9, respectively). The trans isomer 8 is obtained as a sin gle product by heating the mixture of isomers in toluene or, in one st ep, by carrying out the reaction of I with PPh3 in refluxing toluene. Treatment of 8 with TICIO4 in NCMe gives trans-[Pt(C <^> P)(PPh3)(NCMe )]ClO4 10 which can also be obtained by the reaction of 2 with PPh3. C omplex 10 reacts with Ph3P=C(H)R (R = COMe, COOMe, CN) in a 1:1 molar ratio resulting in the displacement of the NCMe ligand and the formati on of [Pt(C <^> P)Cl{C(H)(R')= C(H)PPh3}PPh3]ClO4 (R' = Me 11, OMe 12) or [Pt(C <^> P) {NC-C(H)=PPh3}PPh3]ClO4 13 in which the ylide ligand is selectively O- (11, 12) or N-coordinated (13). The reaction of [Pt( C<^> P)(mu-Cl)](2) 1 with Ph3P=C(H)R (R = COMe, COOMe, CN) in a 1:2 mo lar ratio results in the cleavage of the chlorine-bridge system and th e formation of [Pt(C <^> P)Cl{C(H)(R)PPh3}] (R = COMe 14, COOMe 15, CN 16) as single isomers in which the ylide is C-coordinated ti ans to t he P atom of the C<^>P ligand. Complex 14 reacts with TICIO4 and Ph3P= C(H)COMe (1:1:1 molar ratio) giving [Pt(C <^> P){OC(Me)=C(H)PPh3}(2)]C lO4 17. Complex 17 shows two interesting features: the isomerization o f the C-linked ylide in 14 to an O-bonded one in 17 and the simultaneo us presence of two O-coordinated ylides to the same metal center. The selectivity in the observed coordination modes and the preferred coord ination of the ylides trans to the P atom of the C<^>P ligand are disc ussed in terms of electronic and steric factors. (C) 1998 Elsevier Sci ence S.A. All rights reserved.