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.