J . A m . Chem. SOC.1988, 110, 5931-5932
593 1
AM1-optimized geometry which gave I3C hfs of -22.2 and +16.5 G for H C E C ~ ~ C O ; and HCZ~~CCO;, re~pectively,~~ and with an experimental value of -13.3 G measured for C ~ H S ~ ~ in CO~' an acetyl benzoyl peroxide single crystal at 35-40 K.26 The peroxide precursors of 1 and 2 were also subjected to 308 nm LFP and were found to yield transient absorptions in the visible region of the spectrum, as we have found previously for aroyloxy17 and alkoxycarbonyloxy18 radicals. We assign these absorptions to the expected alkenylcarbonyloxyl md alkynylcarbonyloxyl radicals for the usual reasons, e.g., "instantaneous" (Q4 ns) formation following LFP, lifetimes that are the same in N,-saturated as in 02-saturated solutions, et^.^,* LFP measurement^^,^ indicate that the alkenylcarbonyloxyl radical is of comparable reactivity to benzoyl~xyl~~ and that the alkynylcarbonyloxyl radical has a reactivity greater than benzoyl~xyl~~ but generally somewhat lower than alkoxycarbonyloxy18 radicals. For example, in CCI, 370 535 700 at ambient temperatures the bimoleuclar rate constants for reWavelength (rim) actions of trans-Me3CCH=CHCO2*, C6HSCO2*,Me,CC= CCO;, and CH3CH2CH20C02'with styrene are 0.33, 0.51, 5.3, Figure 1. Corrected emission spectra of (A) M Pt2(P20SH2)44and M Pt2(P205H,)44-and M TINO', both in deoxygenated (B) and 20 X IO8 M-I s-', respectively, and with 1,4-cyclohexadiene water a t room temperature. About 5% of the 514-nm band appears 1.3, 0.66, 9.2, and 9.9 X lo8 M-' s-', respectively. As before,8 superimposed on the 565-nm band in (B). The absorption (and corrected we attribute differences in the reactivities of different XC02' emission) spectra for (A) and (B) are nearly identical. radicals to variations in the importance that polar, canonical structures (e.g., [XC02- RH'+] *) contribute to the stabilization (2,9-dimethyl-4,7-diphenyl- 1,lO-phenanthroline), and various of the transition state for the reaction. Lewis bases.8 However, there have been recent reports of luThe detection of carbonyloxyl radicals by EPR spectroscopy minescent triplet exciplex formation involving rhenium (4,7-diunder normal experimental conditions opens a new avenue for the methyl- l,l0-phenanthroline)(CO),C1 and N,N-dimethylexploration of the chemical and spectroscopic properties of these benzeneamine in decahydronaphthalene solution9 and ruthenium highly reactive and industrially important species. (2,2'-bi~yridine),~+ and Ag' in aqueous solution.I0 Evidence is presented here for the formation of a strongly luminescent triplet exciplex involving Pt2(P205H2)," (Pt,; singlet (25),For HCC=CC02' the AM1-optimized geometr of the carboxyl moiety is r ( C - 0 ) = 1.343 and 1.235 A, r(C-C) = 1.423 and
