126018-99-3Relevant academic research and scientific papers
Synthesis, structural properties, and reaction chemistry of hydrido alkyl diaminocarbene complexes of platinum(II). Cleavage of the metal-carbene and metal-alkyl bonds and synthesis of formamidines and cis hydrido carbene derivatives
Michelin, Rino A.,Bertani, Roberta,Mozzon, Mirto,Zanotto, Livio,Benetollo, Franco,Bombieri, Gabriella
, p. 1449 - 1459 (2008/10/08)
Hydrido alkyl carbene complexes of the type PtH(RX)[C(N(CH2)nCH2)NHR](PPh 3) (n = 2, RX = CF3 (1), CH2CN (2), CH2CF3 (3); n = 4, RX = CF3 (4); R = p-MeOC6H4) have been prepared by reaction of the parent isocyanide precursors PtH(RX)(CNR)(PPh3) with azetidine or piperidine. Complexes 1-4 have cis Pt-H and Pt-RX bonds with the carbene ligand trans to hydride. They have been characterized by analytical data and their IR and 1H, 19F, 31P, and 13C NMR spectra. Compound 2 was also structurally characterized by X-ray analysis. The triclinic crystal, space group P1, has lattice parameters a = 12.998 (3) ?, b = 11.833 (2) ?, c = 10.257 (2) ?, α = 100.83 (4)°, β = 80.72 (3)°, γ = 114.20 (4)°, and Z = 2. The structure was refined to R = 0.022 and Rw = 0.022. The coordination geometry around the Pt atom in 2 is distorted square planar. The geometry of the carbene ligand is essentially planar. The plane of the carbene intersects the platinum square plane at an angle of 73.7 (2)°. The molecules of 2 are associated in the solid state to give dimers through intermolecular interactions between the nitrogen atom of CH2CN and the aminocarbene proton of an adjacent molecule. Important bond lengths are Pt-C(carbene) = 2.069 (4) ?, Pt-H = 1.61 (4) ?, Pt-CH2CN = 2.116 (7) ?, and Pt-P = 2.252 (2) ?. The isocyanide complex PtH(CF3)(CNR)(PPh3) reacts with excess HNEt2 in refluxing THF for 3 days to give a mixture of isomers with the carbene ligand trans to hydride (5a), PPh3 (5b), or trifluoromethyl (5c). Complexes 1-5 are stable in the solid state and in solution, and no reductive elimination of HRX is observed in refluxing THF for several hours even in the presence of diphenylacetylene. However, complexes 2 and 3, but not 1 and 4, react with equivalent amounts of PPh3 to give trans-(PPh3)2PtH[C(NCH2CH2CH 2)NR] (6) and formation of CH3CN and CH3CF3, respectively. Isotopic experiments with N-D and Pt-D derivatives indicate that this reaction proceeds through the protonolysis of the metal-alkyl bond by the aminocarbene proton, promoted by PPh3. Complex 6 reacts with HBF4 to give the hydrido carbene derivative trans-{(PPh3)2PtH[C(NCH2CH2CH 2)NHR]}BF4 (7). Similarly the reactions of 2 with equimolar amounts of diphosphines yield (P-P)PtH[C(NCH2CH2CH2)NR] (P-P = Ph2PCH2CH2PPh2 (8), Ph2PCH=CHPPh2 (9)) and CH3CN. Complexes 8 and 9 react with HBF4 to produce the cis hydrido carbene derivatives {(P-P)PtH[C(NCH2CH2CH2)NHR]}BF4 (10 and 11, respectively). On the other hand, complexes 1 and 4 react with diphosphines to give metal-carbene bond cleavage and formation of (P-P)PtH(CF3) and the formamidines HC(NCH2CH2CH2)=N(R) and HC[N(CH2)4CH2]=N(R), respectively.
