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, PAr₃^F, to give fac-Re(CO)₃(κ²-P,N-S-PNO)(PAr₃^F)]BF₄, 5. Attempts to form a macrocyclic ligand through addition of base to fac-Re(CO)₃(κ²-P,N-S-PNO)(PAr₃^F)]BF₄ were unsuccessful due to loss of PAr₃^F 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.