STEREOCHEMICAL AND ELECTRONIC CONTROL OF FUNCTIONALIZED TRIPODAL PHOSPHINES - REACTIVITY OF THE ADAMANTANE-TYPE IR(TRIPOD)(CO)CL IPOD=CIS,CIS-1,3,5-(PPH(2))(3)-1,3,5-X(3)C(6)H(6), X=H, COOME, CN) COMPLEXES TOWARD H-2, CO, AND C2H4(, H)

Treatment of the tripodal phosphine ligand lphosphino)-1,3,5-tris(meth oxycarbonyl)cyclohexane (tdppcyme) (2) with Ir(PPh(3))(2)(CO)Cl gives the carbonyl chloro complex Ir(tdppcyme)(CO)Cl (2a). NMR spectroscopic investigations prove a dynamic equilibrium between a square-planar (2 a') and a trigonal-bipyramidal (2a) complex with two and three phosphi ne groups coordinated to iridium, respectively. This is in contrast to the comparable complexes Ir(tripod)(CO)Cl (1a, 3a) [tripod = cis,cis- 1,3,5-tris(diphenylphosphino)cyclohexane (tdppcy) (1), o-cis,cis-1,3,5 -tris(diphenylphosphino)cyclohexane (tdppcycn) (3)] which only exist i n the trigonal-bipyramidal form. The three compounds Ir(tripod)(CO)Cl (1a-3a), which only differ in the functionalization of the ligand back bone, display altered basicity and thus different reaction patterns. T he carbonyl chloro complexes 1a-3a are readily protonated by the stron g acid HBF4 to give the octahedral cations 1b-3b. The weaker acid NH4P F6 is only able to protonate the most basic complex Ir(tdppcy)(CO)Cl ( 1a). While Ir(tdppcycn)(CO)Cl (3a) shows no reaction in the presence o f NH4PF6, 2a is orthometalated to complex 2f'. The compounds Ir(tdppcy )(CO)Cl (1a) and Ir(tdppcycn)(CO)Cl (3a) oxidatively add H-2 with diss ociation of Cl- to yield the octahedral dihydrides [Ir(tripod)(CO)(H)( 2)]Cl (1c', 3c'). Under the same conditions a phosphine arm dissociate s from 2a to form the dihydride Ir(eta(2)-tdppcyme)(CO)(H)(2)Cl (2c'). In a CO atmosphere the Ir(tripod)(CO)Cl (1a-3a) complexes give the di carbonyl derivatives [Ir(tripod)(CO)(2)]Cl (1d'-3d'). The dicarbonyls 2d' and 3d' are in an equilibrium with their starting materials. Repla cement of the Cl- by BPh(4)(-) allows the isolation of all three dicar bonyl complexes. Treatment of 1a-3a with ethylene in the presence of N aBPh(4) gives the ethylene complexes [Ir(tripod)(CO)(C2H4)]BPh(4) (1e- 3e). Variable-temperature NMR studies show that there is an exchange p rocess which equilibrates the equatorial with the apical phosphorus nu clei while the CO and ethylene ligands remain rigid. In the cases of 2 e and 3e a second dynamic process with a low-energy barrier exists. Ab ove 45 and 35 degrees C, respectively, 1e and 2e lose ethylene and are orthometalated to 1f and 2f. The cyclometalated products 1f and 2f ca n also be obtained by the direct reaction of 1a and 2a with NaBPh(4). For the dicarbonyl complex 3a and the orthometalated product 2f X-ray structure determinations have been performed.