Thomas H. Tulip

Preparations and reactions of some hydridodinitrogentrialkylphosphine complexes of rhodium(i). The structure of a dinitrogen-bridged rhodium(i) dimer, [RhH(P(i-Pr)3)2]2(μ-N2)

Abstract The reduction of RhCl 3 - 3 H 2 O by sodium amalgam in THF solution under an atmosphere of N 2 and in the presence of an excess of a phosphine ligand has resulted in the formation of the hydridodinitrogen complexes RhH(N 2 )-(PPh(t-Bu) 2 ) 2 (I), RhH(N 2 )(P(t-Bu) 3 ) 2 (II), and [RhH(P(cyclo-C 6 H 11 ) 3 ) 2 ] 2 (μ-N 2 )(V), and a hydridotrisphosphine complex RhH(P(i-Pr) 3 ) 3 (X). The dinitrogen coordination is stable in I but N 2 is readily lost from other dinitrogen complexes, permitting the isolation of three-coordinate hydridobisphosphine rhodium(I) complexes RhH(P(t-Bu) 3 ) 2 (VII) and RhH(P(cyclo-C 6 H 11 ) 3 ) 2 (VIII). Trihydrido complexes RhH 3 L 2 (L = PPh(t-Bu) 2 (XI), P(t-Bu) 3 (XII), P(cyclo-C 6 H 11 ) 2 (XIII), and P(i-Pr) 3 (XIV)) have been synthesized by the reaction of the above rhodium (I) compounds with H 2 . By treatment of the corresponding trihydrido complexes with N 2 we have been able to obtain RhH(N 2 )-(P(cyclo-C 6 H 11 ) 3 ) 2 (III) and RhH(N 2 )(P(i-Pr) 3 ) 2 (IV). Loss of N 2 from IV results in the formation of [RhH(P(i-Pr) 3 ) 2 ] 2 (μ-N 2 ) (VI) and RhH(P(i-Pr) 3 ) 2 (IX). The crystal and molecular structure of [RhH(P(i-Pr) 3 ) 2 ] 2 (μ-N 2 ) (VI) has been determined at —85°C. The compound crystallizes in the triclinic space group C P 1 with two molecules in a cell dimensions a 12.703(16), b 16.455(16), c 11.389(8) A, α 90.25(9), β 103.87(3), γ 97.58(3)°, V 2289 A 3 . The final conventional and weighted agreement indices on F o for F o 2 τ3σ( F o 2 ) are 0.051 and 0.060, respectively. The dinitrogen ligand of VI linearly bridges two planar RhHP 2 fragments with NN separation of 1.134(5) A and an average RhN bond distance of 1.977(6) A. The dihedral angle between the two RhHP 2 fragments is 55.2°. Overall, the dimeric complex effectively has D 2 (222) symmetry.

The structure of trans-chloro(dinitrogen)bis(tri-isopropylphosphine)-rhodium(I): an X-ray study of the structure in the solid state and a nuclear magnetic resonance study of the structure in solution

The crystal structure of [RhCl(N2)(PPri3)2] has been redetermined at –160 °C. In contrast to the results of a previous structure determination, we conclude that a scattering model in which the N2 ligand is end-on (η1) co-ordinated is fully consistent with the data. Such end-on co-ordination is confirmed in solution at +30 °C from the 31P and 15N n.m.r. spectra of a 15N2 labelled sample. The material crystallizes in the space group P21/c(C52h) of the monoclinic system in a cell of dimensions a= 8.062(2), b= 8.883(2), c= 16.431(4)A, β= 92.45(1)°, Z= 2; the final R and R′ are 0.024 and 0.031, respectively, based on the full-matrix refinement of 124 variables and 3 597 observations. The 31P n.m.r. spectrum of the 15N2-labelled complex shows a doublet of doublets, JP – Rh 122.3 and Jp–15N 4.25 Hz, and proves the N2 co-ordination to be η1 in solution. The 15N n.m.r. spectrum of the labelled complex is also consistent with η1-co-ordination: J15N(1)–Rh 28, J15N(1)–15N(2) 4, J15N(1)–P 4, J15N(2)–Rh 4 Hz; δN(1) 269 and δN(2) 302 p.p.m.(downfield from external 15NH4+).

The [Rh(NO)2(PPh3)2]+ catalyzed reaction 2NO + CO → N2O + CO2

Abstract The reaction 2NO + CO → N 2 O + CO 2 has been found to be catalyzed by [Rh(NO) 2 (PPh 3 ) 2 ] in N,N -dimethylformamide (DMF) solution. The rate expression and thermodynamic quantities found are consistent with a mechanism involving a dirhodium species and DMF.