Photochemically activated [MO(CO)(6)] and [MO(CO)(4)(eta(4)-nbd)] have been demonstrated to be very effective catalysts for hydrosilylation of norbornadiene (nbd) by tertiary (Et3SiH, Cl3SiH) and secondary (Et2SiH2 and Ph2SiH2) silanes to give 5-silyl-2-norbornene, which under the same reaction conditions transform in ring-opening metathesis polymerization (ROMP) to unsaturated polymers and to a double hydrosilylation product, 2,6-bis(silyl)norbornane. The yield of a particular reaction depends very strongly on the kind of silane involved. The reaction products were identified by means of chromatography (GC-MS) and 1 H and C-13 NMR spectroscopy. In photochemical reaction of [MO(CO)(4)(eta(4)-nbd)] and Ph2SiH2 in cyclohexane-d(12), eta(2)-coordination of the Si-H bond to the molybdenum atom is supported by H-1 NMR spectroscopy due to the detection of two equal-intensity doublets with (2)J(H-H) = 5.4 Hz at delta 6.12 and -5.86 ppm. (C) 2008 Elsevier B.V. All rights reserved.