The molybdenum trihydrido complexes, H3{[Ph2PCH2-CH2P(Ph)C6H4-o](2)(Ar
)Si-P,P,P,P,Si}], which were readily formed by the thermal reaction of
[MoH4(Ph2PCH2CH2PPh2)(2)] with arylsilanes, reacted with molecular di
oxygen to give the unprecedented molybdenum(IV) peroxo type eta(2)-O-2
complexes, [MoH{[Ph2PCH2CH2P(Ph)C6H4-o](2)(Ar)Si-P,P,P,P,Si} (eta(2)-
O-2)], the structure of which were studied spectroscopically as well a
s X-ray crystallographically.