Photoreaction of diaminosubstituted-phosphiteborane, BH 3 P(NMeCH 2 ) 2 (OMe) with a methyl molybdenum complex, (η 5 -C 5 R 5 )Mo(CO) 3 Me (R 5 =Me 5 , Me 4 H, H 5 ) yielded a phosphiteboryl molybdenum complex, (η 5 -C 5 R 5 )Mo(CO) 3 BH 2 {P(NMeCH 2 ) 2 (OMe)} (R 5 =Me 5 : 2, Me 4 H: 3, H 5 : 4). In the reaction of 2 with MeI, the Mo–B bond was activated to give (η 5 -C 5 Me 5 )Mo(CO) 3 Me, in the reaction with PMe 3 , the B–P bond was activated to give (η 5 -C 5 Me 5 )Mo(CO) 3 (BH 2 PMe 3 ). Complex 2 in solution was gradually converted into (η 5 -C 5 Me 5 )MoH(CO) 2 {P(NMeCH 2 ) 2 (OMe)} (8) via the B–H bond activation of 2. Structures of 2, 3, and 8 were determined by single crystal X-ray diffraction studies.