Coordination chemistry of an asymmetric P,N,O tridentate ligand containing primary phosphine, amine and alcohol donors

The asymmetric, heterodonor tridentate ligand 2(S)-amino-4-phosphinobutan-1-ol, S-PNO, has been prepared from (S)-aspartic acid and some aspects of its coordination chemistry with a number of metal complexes investigated. Reaction of S-PNO with appropriate metal precursors led to the isolation of the complexes fac-Cr(CO)3(κ3-S-PNO), 1, fac-[Mn(CO)3(κ3-S-PNO)]PF6, 2, and fac-[Re(CO)3(κ3-S-PNO)]BF4, 3. The alcohol and amine donors in fac-Cr(CO)3(κ3-S-PNO) were substituted upon addition of trivinylphosphine to 1 to give the complex fac-Cr(CO)3(κ1-P-S-PNO){P(C2H3)3}2, 4. Addition of base to 4 gave a coordinated linear tridentate P3 ligand through the formation of two new chelate rings via hydrophosphination of one vinyl group on each coordinated P(C2H3)3 with the P–H bonds of the complexed S-PNO. The alcohol donor in fac-[Re(CO)3(κ3-S-PNO)]BF4 is labile and can be substituted with tris(2-fluorophenyl)phosphine, PAr3F, to give fac-[Re(CO)3(κ2-P,N-S-PNO)(PAr3F)]BF4, 5. Attempts to form a macrocyclic ligand through addition of base to fac-[Re(CO)3(κ2-P,N-S-PNO)(PAr3F)]BF4 were unsuccessful due to loss of PAr3F prior to any ring-closure. All the complexes have been fully characterised by spectroscopic and analytical techniques including a single-crystal X-ray structure analysis of 2.

The asymmetric, heterodonor tridentate ligand 2(S)-amino-4-phosphinobutan-1-ol, S-PNO, has been prepared and coordinated in κ3 fashion to Cr(0), Mn(I) and Re(I). The alcohol and amine donors in fac-Cr(CO)3(κ3-S-PNO) were substituted upon addition of trivinylphosphine to give the complex fac-Cr(CO)3(κ1-P-S-PNO){P(C2H3)3}2 which underwent base-catalysed formation of two new chelate rings to give a coordinated linear P3 ligand with pendant amine and alcohol groups.Figure optionsDownload as PowerPoint slideHighlights
► A chiral, heterodonor PNO ligand containing primary phosphine, amine and alcohol functions has been coordinated to a number of middle transition metals.
► The alcohol and amine donors are weakly bound and easily replaced by functionalised monophosphines.
► Linear P3 tridentate systems with pendant amine and alcohol functions are synthesised by the coupling of vinyl groups on coordinated trivinylphosphine with the P–H functions of the heterodonor ligand on chromium(0).