SYNTHESIS, CHARACTERIZATION, AND REACTIONS OF RHODIUM(I) AND IRIDIUM(I) BIS(IMINOPHOSPHORANYL)METHANIDE COMPLEXES IN WHICH THE LIGAND ACTS AS A SIGMA-N,SIGMA-C CHELATE - X-RAY CRYSTAL-STRUCTURE OF [IR(CH(PPH2=N-C6H4-CH3-4)2)(COD)]

Reaction of the lithium-bis(iminophosphoranyl)methanide compounds Li[C H(PPh2=N-C6H4-R'-4)2] (2a, R' = CH3; 2b, R' = CH3 and NO2; 2c, R' = NO 2) with [ML2Cl]2 (M = Rh, L2 = COD, L = CO; M = Ir, L2 = COD) yields t he novel bis(iminophosphoranyl)methanide complexes [M{CH-(PPh2=N-C6H4- R'-4)2}L2] (3a-d, 4a-c), in which the ligand is coordinated as a sigma -N,sigma-C chelate. Complex 3a (M = Rh, R' = CH3, L2 = COD) has also b een synthesized in the reaction of CH2-(PPh2=N-Cr6H4-CH3-4)2 (1a) with [Rh(COD)(OMe}]2. The COD ligand in the It-COD compounds 4a-c can be s ubstituted by reaction with CO to give[Ir(CH(PPh2=N-C6H4-R')2}(CO)2] ( 4d-f). The solid-state structure of 4a (M = Ir, R'= CH3, L2 = COD) has been determined by an X-ray diffraction study. Compound 4a crystalliz es in the triclinic space group P1BAR with a = 10.633 (2) angstrom, b = 11.766 (2) angstrom, c = 17.366 (2) angstrom, alpha = 99.73 (1)-degr ees, beta = 90.59 (3)-degrees, gamma = 95.42 (2)-degrees, and Z = 2. T he structure was refined to R = 0.055 (R(w) = 0.060) using 4065 indepe ndent observed reflections. The bis-(iminophosphoranyl)methanide ligan d is coordinated in a sigma-N,sigma-C chelate mode toward the square p lanar Ir, giving rise to a four-membered M-N-P-C metallacycle and one pendant iminophosphorane moiety. Important bond distances and angles a re P1-N1 = 1.55 (1) angstrom, P2-N2 = 1.62 (1) angstrom, P1-C1 = 1.82 (1) angstrom, P2-C1 = 1.77 (1) angstrom, ir-C1 = 2.16 (1) angstrom, an d Ir-N2 = 2.07 (1) A, and N2-Ir-C1 = 73.4 (4)-degrees, C1-PI-N1 = 119. 3 (6)-degrees, and Cl-P2-N2 = 96.4 (5)-degrees. In solution the bis(im inophosphoranyl)methanide complexes undergo a dynamic process, in whic h both halves of the ligand and both coligands become equivalent. The exchange processes for 3a, 3b, 4a, and 4d have been studied by using v ariable-temperature H-1 and P-31 NMR; they occur via a Berry pseudorot ation, involving an intermediate five-coordinate complex that is forme d via intramolecular attack of the pendant iminophosphorane entity. Ad ditional structural information has been acquired from IR and C-13, Rh -103, and solid state P-31 {H-1}CP/MASNMR spectroscopy. Complexes 3a, 3b, 4a, and 4d react with CO2 in an aza-Wittig reaction to give the (i minophosphoranyl) (oxophosphoranyl)methyl complexes [M{CH(PPh2 = N-C6H 4-CH3-4)(PPh2 = O)}L2](5a-d),p-tolylisocyanate, and di-p-tolylcarbodii mide. The inertness of the four membered M-N-P-C ring toward CO2 stres ses the nonreactivity of this polarized metallacycle. Treatment with C F3COOH results in direct protonation of the nitrogen atom of the free iminophosphorane moiety, affording the complexes [M{CH-(PPh2 = N-C6H4- CH3-4)(PPh2-NH-Cr6H4-CH3-4)IL2]+X- (II). Reaction with HCI leads to a net protonation of either the methanide or the nitrogen atoms with for mation of the known coordination complexes of bis(iminophosphoranyl)me thane, in which the ligand is either coordinated as a sigma- N, sigma- C chelate (in II) or as a sigma-N, sigma-N' chelate in [M{(4-CH3-C6H4- N = PPh2)2CH2}-L2]+X- (III), respectively. This reaction proceeds via initial oxidative addition of HCI to Rh or Ir and a subsequent hydroge n-migration reaction from the metal to either the methanide C atom or the N atom of the coordinated iminophosphorane entity. This has been e videnced by the observation of Ir-hydride complexes (H-1 NMR) in the r eaction of 4a with 1 equiv of HCI at 193 K. These complexes react furt her to give II and III upon raising the temperature to 233 K. Addition of excess HX (X = CF3COO, Cl) to the bis(iminophosphoranyl)methanide complexes 3a, 3b, 4a, and 4d gives [ML2X]2 and the amino[(aminophospho nio)methyl]phosphonium compounds [CH2-(PPh2-NH-C6H4-CH3-4)2]2+.2X- (IV ).