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Theoretical Studies of Oxidative Addition of E−E Bonds (E = S, Se, Te) to Palladium(0) and Platinum(0) Complexes

2005; American Chemical Society; Volume: 24; Issue: 21 Linguagem: Inglês

10.1021/om050023s

1520-6041

Jason M. Gonzales, Djamaladdin G. Musaev, Keiji Morokuma,

Asymmetric Hydrogenation and Catalysis

The density functional method has been applied to investigate the mechanism and controlling factors of RE−ER (R = H, Me and E = S, Se, Te) oxidative addition to M(PR3')2 complexes (where M = Pd, Pt and R' = H, Me), which is proposed to be the first step of Pd(0)- and Pt(0)-catalyzed E−E addition to CC and C⋮C bonds. In general, it was shown that the energy of E−E activation correlates with the E−E bonding energy and decreases via the sequence E = S > Se > Te, for all R, R' and transition-metal atoms used; the weaker the E−E bond, the smaller the oxidative addition barrier. The exothermicity of this reaction also decreases via the same trend, E = S > Se > Te, and correlates with the decrease in M−ER bond strength. Meanwhile, the E−E activation barrier is found to be higher for M = Pt than for M = Pd, while for all studied R, R', and E the reaction is found to be more exothermic for M = Pt than for M = Pd. It was shown that the more the methyl substitution in the systems (both in substrate and the catalyst), the larger the E−E activation barrier. Calculations of the energetics of the reaction cis-(PR'3)2Pd(ER)2 → cis-(PR'3)Pd(ER)2 + PR'3 show that PR'3 dissociation energy from the cis-(PR'3)2Pd(ER)2 complex decreases (a) via the sequence E = S > Se > Te for given M and R = R' and (b) via the trend M = Pt > Pd for given E and R = R'. The exothermicity of dimerization of the cis-(PR'3)M(ER)2 intermediate decreases via the sequence E = S > Se >Te and increases via M = Pd < Pt for R = R' = H.