Finally, it should be noted that the $=diene-carbonyl complex (20) requires somewhat more forcing conditions for its preparation than do the related phosphine compounds (18 and 19). Thus, when L = CO in' reaction 8, a hexanes solution of the organometallic reactant must be subjected to 60 psig of carbon monoxide at room temperature for 5 days in order to effect complete conversion. This observation again gives a clear indication of the relatively high inertness of the Mo-~~-trans-diene linkage in 8 to undergo substitution reactions. Even more surprising is the fact that no CpMo(NO)(CO),, the disubstituted product, is formed during this transformation.Clearly, further studies of the characteristic reactivities of compounds 1-14 must be effected so that their chemical properties can be discussed in the proper context. Such studies are currently in progress. Acknowledgment.We are grateful to the Natural Sciences and Engineering Research Council of Canada for support of this work in the form of grants to P.L. and a graduate scholarship to A.D.H. We also thank Professor Bruce E. Bursten for numerous stimulating discussions.Treatment of solutions of the 16-electron dialkyl compounds Cp'M(NO)R2 (Cp' = Cp (q5-C5H5) or Cp* ( T~-C~M~~) ; M = Mo or W; R = CH2SiMe3, CH2CMe3, CH2CMe2Ph, CH2Ph, or Me) with either dioxygen or aqueous hydrogen peroxide in Et20 at ambient temperatures and pressures produces novel dioxo alkyl complexes CP'M(O)~R which can be isolated in moderate yields (45430%). The results of labeling studies with l8Oz are consistent with the first steps of the reactions involving O2 proceeding via the coordination of the diatomic molecule to the metal centers in the organometallic reactants. The preferred sites of reactivity in the dioxo alkyl complexes are their M=O linkages. Thus, exposure to 30% Hz02 in Et20 converts them cleanly to the oxo peroxo derivatives Cp'M(0)(a2-02)R and treatment of representative CP'W(O)~R species with HC1 (or PC15 or Me3SiC1) in EtzO produces the corresponding Cp'W(O)(Cl),R compounds in high yields. These dichloro oxo complexes are very useful synthetic precursors in their own right, undergoing metathesis with alkyllithium or alkyl Grignard reagents to produce the oxo trialkyl compounds Cp'W-(O)R,R',, in which R and R' represent selected alkyl groups. Sterically crowded members of this class of compounds are not isolable under ambient conditions since they spontaneously convert to the corresponding oxo alkylidene species, presumably via intramolecular a-H abstraction. The isolable oxo trialkyl complexes can be induced to undergo the same conversions simply by gentle warming of their solutions. All the new oxo complexes isolated during this work have been fully characterized by conventional spectroscopic techniques. Their physical properties indicate that they are all monomeric 16-valence-electron species possessing piano-stool molecular structures and containing the metal in its highest oxidation state of +6. (4) (a) Herrmann, W. A.; Serrano, R.; Bock, H. Angew. Chem., Int. Ed. Eng...

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Protonic acids such as H202(aq) or HCI in Et20 transform one of the M=O linkages and not the M-C B bonds of CP'M(O)~R complexes [Cp' = Cp (v5-C5H5) or Cp" (v5-C5Me5); M = Mo or W; R = CH2SiMe3 or Me].The respective oxo peroxo and oxo dichloro product complexes Cp'M(0)(v2-02)R and Cp * W(O)(CI),R are isolable in good yields as air-stable crystalline solids that have been fully characterized by conventional methods, including a single-crystal X-ray crystallographic analysis of

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