GROUP-9 METAL 1,1'-BIS(PHOSPHINO)FERROCENE COMPLEXES - SYNTHESIS, STRUCTURES, SOLUTION CONFORMATION AND UNUSUAL REACTIVITY

The crystal structure of [Ir(cod)(L-L)](+) 3 [cod = cycloocta-1,5-dien e, L-L = opropylphosphino)-1'-(diphenylphosphino)ferrocene] can be rel ated to those of the analogous complexes with L-L - 1,1'-bis(diphenylp hosphino)ferrocene (dppf) 1 and 1,1'-bis(diisoprophylphosphino)ferroce ne (disppf), 2, all the complexes being readily synthesized from [Ir(c od)(py)(2)](+) (py = pyridine). An optimum diphosphine bite angle of a pproximately 99 degrees is maintained in all three complexes by varyin g the twist of the ferrocene, which decreases with increasing steric p rofile of the phosphine, and by distortion of the geometry at the irid ium atom away from square planar towards tetrahedral. The twist about the ferrocene moiety induces chirality at the iridium atom in all thre e complexes and the interchange of stereoisomers can be followed by va riable-temperature H-1 NMR spectroscopy. Application of the Eyring equ ation gave approximate values of Delta G(double dagger)for this proces s of 36.1 +/- 0.2, 39.3 +/- 0.2 and 34.3 +/- 0.2 kJ mol(-1) for 1-3 re spectively. The ligand disoppf also induces considerable distortion aw ay from square-planar geometry in the complex [Rh(nbd)(disoppf)][BF4] 4 {nbd = norbornadiene (bicyclo[2.2.1]hepta-2,5-diene)}, as found in a crystal structure determination, which may account for the unusual la bility of the chelating diphosphine. This is demonstrated by its react ions with Ph(2)P(CH2)(n)PPh(2) (n = 1 or 2) both of which give [Rh(L-L )(2)](+). More surprisingly, considering its lability in [Rh(nbd)(dppf )](+), dppf also readily displaced disoppf from 4, to give [Rh(nbd)(dp pf)][BF4] 5. The nbd ligand in this complex is not displaced by reacti on with an excess of dppf.