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

The complex [Rh(CO)2{HC(pzʹ)3}][PF6], 1+[PF6]-{HC(pzʹ)3= tris(3,5-dimethylpyrazolyl)methane}, prepared by reacting [{Rh(CO)2(µ-Cl)}2] with HC(pzʹ)3 in the presence of Tl[PF6], has a distorted square pyramidal structure with a (kappa)3-HC(pzʹ)3 ligand. Carbonyl substitution with Lewis bases gives [Rh(CO)L{HC(pzʹ)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(pzʹ)3}]2+, 22+, and [Rh(CO)(AsPh3){HC(pzʹ) 3}]2+, 32+, characterised by ESR spectroscopy. Complex 1+[PF6]-reacts with PhC(identical)CPh to give [Rh(CO)((eta)2-PhC(identical) CPh){HC(pzʹ)3}][PF6], 5+[PF6]-, in which the two-electron donor alkyne occupies an equatorial position in a trigonal bipyramidal (kappa)^3 structure. With MeC(identical)CR (R = Me or Et), 1+[PF6]- gives the (kappa)^2 square planar complexes [Rh{(eta)4C4Me2R2C(O)}{HC(pzʹ)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(identical)CPh or HC(identical)CH, 1+ gives the octahedral, (kappa)^3 rhodium(III) metallacyclopentadienes [Rh(CO)((eta)1:(eta)1ʹ-CHCRCHCR){HC(pzʹ)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(identical)also gives the cycloheptatrienone (tropone) derivative [Rh{(eta)4-C6H6C (O)}{HC(pzʹ)3}][PF6], 10+[PF6]-, with a (kappa)^3 ligand and the cycloheptatrienone ligand bound to the metal via two Rh-C (sigma)bonds and one Rh-monoalkene interaction.