| Abstrakt: |
Six dangling phosphine complexes have been synthesized to provide three pairs of linkage isomers, (OC)5M[η1-PPh2CH2CH2P(p-tolyl)2] (3Cr, 3Mo, 3W) and (OC)5M[η1-P(p-tolyl)2CH2CH2PPh2] (4Cr, 4Mo, 4W). Rate constants for isomerization in toluene of 3Cr, 3Mo, 3W, 4Cr, 4Mo, and 4W at 55 °C are 1.23 × 10-8, 7.76 × 10-6, 2.3 × 10-8, 6.52 × 10-9, 4.24 × 10-6, and 9.7 × 10-9 s-1, respectively. Rate constants for chelation of 3Cr, 3Mo, 4Cr, and 4Mo are 1.15 × 10-8, 3.9 × 10-7, 1.23 × 10-8, and 3.9 × 10-7 s-1, respectively. Chelation rates for 3W and 4W were too slow to conveniently measure. The position of equilibrium favors ditolylphosphino coordination with equilibrium constants of 1.88, 1.83, and 2.4 for the Cr, Mo, and W isomer pairs, respectively. Isomerization of 3Mo and 4Mo was studied at 25, 40, and 55 °C to give activation parameters, ΔH&thermod; and ΔS&thermod;, of 102.4 and 103.6 kJ/mol and −32 and −33 J/(K mol), respectively. ΔH&thermod; and ΔS&thermod; for chelation of 3Mo and 4Mo were determined to be 113.5 and 115.5 kJ/mol and −22 and −16 J/(K mol), respectively. These results suggest that the transition states for both isomerization and chelation are significantly associative and become more so in descending order through group 6. |
