DIBENZOTROPYLIDENE PHOSPHANES (TROPPS) - SYNTHESIS AND COINAGE METAL-COMPLEXES

Dibenzocycloheptatrienyl phosphanes (dibenzotropylidene phosphanes = T ROPP(R)) 11a-c may be easily prepared from dibenzocycloheptatrienyl ch loride 8 and the secondary phosphanes R2PH [9a: R = Ph; 9b: R = 4-Me-C 6H4; 9c: R = cyclohexyl (Cyc)] in good yields. Alternatively, the di(t ert-butyl)phosphanyl substituted TROPPBut derivative 4 was obtained al ong with the phosphane 5 by a mechanistically still unknown rearrangem ent of a strained phosphorus ylide I. The conformations of these new p hosphanes were established by X-ray analyses performed for the compoun ds TROPPBut 4 and TROPPPh 11a. The R2P moiety is bonded to an axial po sition of the central seven-membered ring, which adopts a boat conform ation. Thereby a rigid concave binding site containing a phosphane and an olefin function is formed, which should allow the synthesis of a w ide range of transition metal complexes. In order to test how far the particular shape of the TROPP-type ligands enforces metal-olefin inter actions, the coinage metal complexes [(TROPPPh)Cu(mu(2)-Cl)](2), 13, [ (TROPPPh)Ag(mu(2)-O2SOCF3)](2), 16, C(TROPPPh)(2)Ag][O3SCF3], 17 and [ (TROPPPh)AuCl], 19 were prepared. These were completely characterized by multinuclear NMR experiments in solution and the solid state, as we ll as by X-ray analyses. The structural and NMR data show that the int eraction between the metal center M and the olefin moiety of the TROPP ligand is weak and decreases in the order Cu > Ag > Au. Indeed, for 1 9 (M = Au) no interaction could be observed. In the silver complex 17, coupling between an Ag nucleus and a proton of a bonded olefin was de termined for the first time [J(Ag-109/107, H-1) = 0.4 Hz]. In solution the complexes derived from TROPP-type ligands seem to have an enhance d (kinetic) stability.