Iminophosphines: Synthesis, formation of 2,3-dihydro-1 H-benzo[1,3]azaphosphol-3-ium salts and N-(pyridin-2-yl)-2-diphenylphosphinoylaniline, coordination chemistry and applications in platinum group catalyzed Suzuki coupling reactions and hydrosilylations

Article abstract of DOI:10.1016/S0022-328X(02)01203-2

The aprotic and protic bi- and multidentate iminophosphines 2-Ph₂PC₆H₄N=CR¹R² (R¹ = H, R² = Ph = 2a; R¹ = Me R² = Ph = 2b; R¹ = H, R² = 2-thienyl = 2c; R¹ = H, R² = C₆H₄-2-PPh₂ = 2d; R¹ = H, R² = C₆H₄-2-OH = 2e, R¹ + H,R² = C₆H₄-2-OH-3Bu′ = 2f: R¹ = H, R² = CH₂C(O)Me = 2g) have been prepared by the acid catalyzed condensation of 2-(diphenylphosphino)aniline with the corresponding aldehyde-ketone. Iminophosphine 2d can be reduced with sodium cyanoborohydride to give the corresponding amino-diphosphine has been characterized by single-crystal X-ray crystallography, as its palladium dichloride derivative. The attempted condensation of 2-(diphenylphosphino)aniline with pyridine-2-carboxaldehyde to give the corresponding pyridine-functionalized iminophosphine resulted in an unusual transformation involving the diastereoselective addition of two equivalents of aldehyde to give 1,2-dipyridin-2-yl-2-(o-diphenylphosphinoyl) phenylamino-ethanol, which has been characterized by a single-crystal X-ray structure determination. The bidentate iminosphosphine 2-Ph₂PC₆H₄N=C(H)Ph reacts with [(cycloocta-1,5-diene)PdCIX] X = Cl. Me) to give [Pd 2- Ph₂PC₆H₄N-C(H)Ph|CIX] and the imino-diphosphine 2-Ph₂PC₆H₄N=C(H)C₆H₄-PPh₂ reacts with [(cycloocta-1,5-diene)PdClMe] to give [Pd|2-Ph₂PC₆H₄N=C(H)C₆H₄-PPh₂}ClMe] and each has been characterized by single-crystal X-ray crystallography. The monobasic iminophosphine 2-Ph₂PC₆H₄N=C(Me)CH₂C(O)Me reacts with [Ni(PPh₃)₂Cl₂] in the presence of NaH to give the phosphino-ketoiminate complex [Ni{2-Ph₂PC₆H₄N=C(Me)CHC(O)Me}Cl], which has been structurally characterized. Mixtures of iminophosphines 2a-h and a palladium source catalyze the Suzuki cross coupling of 4-bromoacetophenone with phenyl boronic acid. The efficiency of these catalysts show a marked dependence on the palladium source, catalysts formed from [Pd₂(OAc)₆ giving consistently higher conversions than those formed from [Pd₂(dba)₃] and [PdCl₂(MeCN)₂]. Catalysts formed from neutral bi- and terdentate iminophosphines 2a-d gave significantly higher conversions than those formed from their monobasic counterparts 2e-f. Notably, under our conditions the conversions obtained with 2a-c compare favorably with those palladium. In addition, mixtures of [Ir(COD)Cl]₂ and 2a-h are active for the hydrosilytation of acetophenone; in this case catalysts formed from monobasic iminophosphines 2e-f giving the highest conversions.