2‐Phosphanylphosphinines as Bridging Ligands for Dinuclear Transition Metal Carbonyls

The 2‐phosphanyl‐4,5‐dimethylphosphinines 1‐5 are powerful bridging ligands able to stabilize metal‐metal single and triple bonds between low‐valent transition metal centres. Their reaction with Mn 2 (CO) 10 in refluxing xylene yields the corresponding Mn 2 (CO) 8 complexes 6 and 7 . Reaction with [Fe 2 Cp 2 (CO) 4 ] under UV irradiation similarly yields the Fe‐Fe‐bridged Fe 2 Cp 2 (CO) 2 complexes 8 and 9 . An additional observation is that the 2‐phosphininyl‐3,4‐dimethylphosphaferrocene 10 is formed upon reaction of the 2‐phospholylphosphinine 5 with [Fe 2 Cp 2 (CO) 4 ] at high temperature under CO pressure. A clean addition occurs at the Mo≡Mo triple bond of [Mo 2 Cp 2 (CO) 4 ] to give the Mo‐Mo single‐bonded complexes 11 ‐ 15 . The thermolysis of these complexes succeeds when the phosphanyl group is a phosphonite P(OEt) 2 ( 13 ) or P(OAr) 2 ( 14 ), affording cleanly the Mo 2 Cp 2 (CO) 4 triple‐bonded complexes 16 and 17 , respectively. The metal‐metal triple bonds of these complexes readily add two molecules of CO to reform 13 and 14 , or one molecule of t Bu‐N≡C to give 18 and 19 . The X‐ray crystal structure analysis of the MO 2 C 2 (CO) 4 complex 13a , with the 2‐P(OEt) 2 ‐ phosphinine, shows a gauche orientation of the two Cp rings and very short P‐Mo bonds of 2.3565(4) and 2.406(2) Å to the phosphinine and P(OEt) 2 groups, respectively.