Organometallic cluster complexes with face-capping arene ligands, 9. Hydrogenation of the side-chain in [{(C5H5)Co}(3)(mu(3)-alkenylbenzene)]: synthesis and structure of the cluster complexes [{(C5H5)Co}(3)(mu(3)-eta(2)2 :eta(2):eta(2)-C6H5-CHR1-CH2R2)]

Catalytic hydrogenation (1 bar H-2, 20 degrees C, Pd/C catalyst) of the C=C double bond in the side-chain of the facial alkenylbenzene ligands of the cluster complexes [{(C5H5)Co}(3){mu(3)-C6H5(CR1)(CHR2)}] 2b-c gave the deri vatives [{(C5H5)Co}(3){mu(3)-C6H5(CHR1)(CH2R2)}] 3b-d in high yield (b, R-1 = CH3, R-2 = H; c, R-1 = H, R-2 = Ph; d, R-1 = Ph, R-2 = H). The X-ray cry stal and molecular structures of 3c and 3d were determined. In both derivat ives a facial mu(3)-eta(2):eta(2):eta(2) coordination of one phenyl ring to the tricobalt cluster was found. Only one of two possible diastereomeric c onformers is present in the crystals of 3d. The expanded mu(3)-phenyl rings show a small but statistically significant Kekule-type (trigonal) distorti on. In solution hindered rotation of the mu(3)-arenes on top of the [(C5H5) Co](3) clusters is observed by NMR spectroscopy. (C) 1999 Elsevier Science S.A. All rights reserved.