The substitution chemistry of the tris(3,5-dimethylpyrazolyl)-methanerhodium complex [Rh(CO)2{HC(pz′)3}]+

The complex [Rh(CO)(2){HC(pz')(3)}][PF6], 1(+)[PF6](-) {HC(pz')(3) = tris(3,5-dimethylpyrazolyl) methane}, prepared by reacting [{Rh(CO)(2)(mu-Cl)}(2)] with HC(pz')(3) in the presence of Tl[PF6], has a distorted square pyramidal structure with kappa(3)-HC(pz')(3) ligand. Carbonyl substitution with Lewis bases gives [Rh(CO)L{HC(pz')(3)}][PF6] {L = PPh3, 2(+)[PF6](-); L = AsPh3, 3(+)[PF6](-); L = P(o-tolyl)(3), 4(+)[PF6](-)}, which have square planar kappa(2) structures, confirmed by X-ray crystallography for 2(+)[PF6](-). The cations 2(+) and 3(+) have the third pyrazolyl ring orientated pseudo- parallel to the square planar metal whereas 4(+) more likely has the third ring orientated exo to that plane. One-electron oxidation of 2(+) and 3(+) gives the Rh(II) dications [Rh(CO)(PPh3){HC(pz')(3)}](2+), 2(2+), and [Rh(CO)(AsPh3){HC(pz')(3)}](2+), 3(2+), characterised by ESR spectroscopy. Complex 1(+)[PF6](-) reacts with PhC=CPh to give [Rh(CO)(eta(2)-PhC=CPh){ HC(pz')(3)}][PF6], 5(+)[PF6](-), in which the two-electron donor alkyne occupies an equatorial position in a trigonal bipyramidal kappa(3) structure. With MeC=CR (R = Me or Et), 1(+)[PF6](-) gives the kappa(2) square planar complexes [Rh{eta(4)-C4Me2R2C(O)}{HC(pz')(3)}][PF6] (R = Me, 6(+)[PF6](-); R = Et, 7(+)[PF6](-)) in which the cyclopentadienone ligands are coordinated via two Rh-monoalkene bonds; the structurally characterised form of 7(+) has the two alkyne units linked head-to-head with the CEt termini bound to the ketonic CO group. With HC=CPh or HC=CH, 1(+) gives the octahedral, kappa(3) rhodium(III) metallacyclopentadienes [Rh(CO)(eta(1):eta(1')-CHCRCHCR){HC(pz')(3)}][PF6] (R = Ph, 8(+)[PF6](-); R = H, 9(+)[PF6](-)) with the two alkynes linked head-to-tail in 8(+). The reaction of 1(+) with HC=CH also gives the cycloheptatrienone (tropone) derivative [Rh{eta(4)-C6H6C(O)}{HC(pz')(3)}][PF6], 10(+)[PF6](-), with kappa(3) ligand and the cycloheptatrienone ligand bound to the metal via two Rh-C sigma-bonds and one Rh-monoalkene interaction.