New (aminomethyl)phosphines via selective hydrophosphination and/or phosphorus based Mannich condensation reactions

Abstract

Controlled stepwise reaction of a geminal substituted alkene or primary amine group afforded a small library of new functionalised tertiary and ditertiary phosphines. Accordingly, Mannich based condensation of the commercially available disubstituted arene C6H4(NH2){2-C(Me)=CH2} with HOCH2PR2 (R2 = Cg: 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phosphaadamantyl; Ph2) afforded the (aminomethyl)phosphines C6H4(NHCH2PCg){2-C(Me)=CH2} L1 and C6H4(NHCH2PPh2){2-C(Me)=CH2} L2 in approx. 60% yield. In addition to the formation of L2, the diphosphine L3 was also identified and independently synthesised upon reaction of C6H4(NH2){2-C(Me)=CH2} with two equiv. of HOCH2PPh2 in CH3OH under reflux. Alternatively, reaction of C6H4(NH2){2-C(Me)=CH2} with H-PR2 (R2 = Cg or Ph2) in the presence of AIBN [2,2′-azobis(2-methylpropionitrile)] as free radical initiator, afforded the primary amine functionalised phosphines C6H4(NH2){2-CH(Me)CH2PCg} L4 and C6H4(NH2){2-CH(Me)CH2PPh2} L5 in 85% and 66% isolated yields respectively. In both cases only the anti-Markovnikov addition products were observed. Subsequent reaction of L5 with HOCH2PR2 (R2 = Ph2) afforded the unsymmetrical ditertiary phosphine C6H4(NHCH2PPh2){2-CH(Me)CH2PPh2} L6. Some preliminary coordination studies towards [RuCl(μ-Cl)(η6-C10H14)]2, [AuCl(tht)] (tht = tetrahydrothiophene) and [MCl2(η4-cod)] (M = Pd, Pt; cod = cycloocta-1,5-diene) demonstrate these new ligands behave as classic P-donors leaving the pendant amino or alkenyl groups non-coordinating. All compounds have been characterised by multinuclear NMR, FT−IR, mass spectrometry and microanalysis. Single crystal X-ray studies have been performed on L3, L5, L6, 1, 3b·0.5CH2Cl2, 4a·1.5CH2Cl2, 5 and 6·0.5CDCl3·0.5C4H10O.