The photogeneration of the complexes [(q'-GHJM(CO),I 2 (M = 0, Mo, W)and t($-C,(CH&)-M(CO)2] 2 (M = Cr, MO) is reported. These species are formulated as metal-metal triple bonded complexes which can be generated from the corresponding [($-GHs)M(CO)J z and [(~"-Cs(CH,)s)M(COI312 metal-metal single bonded complexes by either irradiation at 25 "C or by heating. All of the triple bonded complexes take up CO at 25 "C to generate the single bonded complexes, but the Cr complexes require high CO pressure, while the MO and W species take up CO at or below one atmosphere with halftimes of less than a minute. The complexes [($-C5-Hs)M(CO)2]2 (M = MO, W) react with a variety of acetylenes at 25 "C to yield complexes having a MzC2 "tetrahedrane-like" core. The mechanism of the formation of the triple bonded complexes from the single bonded complexes is proposed to first involve cleavage of the metal-metal single bond to generate 17-electron intermediates of the formula ($-C5H5)-M(CO), or ($-C,(CH,),)M(CO),. These species are coordinatively labile and lose CO dissociatively yielding 15-electron intermediates which dimerize to give the
triple bonded complexes. B III (1) Addition of PPh3, P(OCH3)3, I*, or acetylenes to III has also been reported [3]. Importantly, the Mo-MO distance in III [3] is -0.8 W shorter than the MO-MO distance in IV [4] which strongly supports the notion that there is a multiple metal-metal bond in III. These studies [2, 31 are among several recent reports [4-71 concerning the chemistry of the species (Q~-C~H~)~M~(CO)~ (M = Cr,.Mo, W). We note the report [5] of the thermal conversion of (TJ'-C~H~)~-Crz(CO)b, Va, or ($-CSH4(CH3))Krz(CO)e, Vb, to (r?-CsH&Cr2(CO)4, Via, and ($GH4(CH&CrZ-(CO),, VIb, respectively, reaction (3). The complex ($-CS(CH3)5)ZCrz(C0)4, VII, is well characterized z @ l. (oc) Cr-cP)3 h e -(3) J 7.