Reactions of Ru 3 (CO) 12 with Diphosphenes — A New Route to 50‐Electron Ru 3 P 2 nido ‐Clusters

The reaction of the symmetric diphosphene 2, 4, 6‐(CF 3 ) 3 ‐C 6 H 2 ‐P=P‐C 6 H 2 ‐2, 4, 6‐(CF 3 ) 3 4 with Ru 3 (CO) 12 led to the 50‐electron Ru 3 P 2 nido ‐cluster Ru 3 (CO) 9 [μ‐P‐C 6 H 2 ‐2, 4, 6‐(CF 3 ) 3 ] 2 5 , which in solution at room temperature displays hindered rotation of the aromatic rings about the C(aryl)—P bonds. The structure of 5 was determined by X‐ray crystal structure analysis; its Ru 3 P 2 centre forms a distorted square pyramid with one ruthenium atom at the apex. One of the two C 6 H 2 (CF 3 ) 3 groups is also appreciably distorted. Temperature‐dependent 19 F NMR studies of the [A 3 M 3 X] 2 spin system (A = M = CF 3 , X = 31 P) of 5 indicated a rotational barrier ΔG ≠ of 82.3 kJ mol ‐1 at 141 °C. The same Ru 3 P 2 core was obtained by the reaction of the unsymmetric diphosphene Mes*‐P=P‐Mes 11 with Ru 3 (CO) 12 ; hindered rotation about the C(aryl)—P bonds was also observed, in this case.