Matrix isolation has been combined with infrared spectroscopy and theoretical calculations to study intermediates formed in the thermal and photochemical reactions of CrCl 2 O 2 with GeH 4 , AsH 3 and H 2 Se in argon matrices. Photochemical reactions occurred for all 3 systems with light of λ>300nm, leading to multiple products with GeH 4 and AsH 3 . For GeH 4 , O atom insertion into a Ge–H bond to form H 3 GeOH complexed to CrCl 2 O was observed, along with a novel product arising from H 2 elimination, H 2 ClGe–O–CrCl 2 O. With AsH 3 , insertion to form the H 2 AsOH–CrCl 2 O complex was observed, along with valence expansion and O atom addition to form the H 3 AsO–CrCl 2 O complex. Product identification came through comparison to theoretical calculations at the B3LYP/6-311++g(d,2p) level, and through isotopic labeling for the arsenic system. Band intensities and product yields were sufficiently low with H 2 Se that only HSeOH–CrCl 2 O could be tentatively identified. Trends for O atom insertion versus O atom addition via valence expansion were explored.