Basische metalle

A Monometallic Rh(III) Tetraphosphine Complex: Reductive Activation of CH2Cl2 and Selective Meso to Racemic Tetraphosphine Ligand Isomerization

“…This might seem to argue against the proposed free radical mechanism for the rhodium complex. The previous work in preparing metal−CH 2 X complexes from the reaction with CH 2 X 2 , however, demonstrates that the mechanism is most consistent with a relatively simple and classic 2e - oxidative addition reaction. ,,, The only evidence we have of a [ rac -Rh(Cl)(CH 2 Cl)(η 4 -et,ph-P4)] + complex being formed is the 13% disordered complex present in the one crystal structure discussed previously. There are no examples that we could find of simple reactions of CH 2 Cl 2 with Group 8 transition metal complexes that form metal dichloride complexes in high yields, such as we see here.…”

“…The synthesis of [RhCl 2 (η 4 -rac-et,ph-P4)] + in high yield in the presence of CH 2 Cl 2 , especially when that is the only source of chlorine atoms, demonstrates that this monometallic complex is formed via the activation of CH 2 Cl 2 . The activation of dihalomethanes by late transition metal complexes has been studied as a method of generating the useful metal−halomethane unit, M−CH 2 X. ,, Occasionally, double activation of the dihalomethane results in the synthesis of bridging methylene (μ-CH 2 ) binuclear complexes. Marder et al, for example, reported the synthesis of trans -[RhCl(CH 2 Cl)(dppe) 2 ] + , 6 , from the reaction of [Rh(dppe) 2 (CH 2 X)] with CH 2 Cl 2 .…”

“…The majority of dihalomethane activation reactions include only a handful of examples with CH 2 Cl 2 , which is usually difficult to activate. Most researchers have concentrated on reactions of the considerably more reactive CH 2 I 2 , CH 2 Br 2 , and CH 2 ICl substrates. 24b,25b, Werner et al conducted elegant studies on the CpRhL 2 half-sandwich complexes and their reactions with CH 2 X 2 (X = Br, I, CN) substrates. Their work demonstrated halide−methylene migrations (e.g., Rh(L)(CH 2 X) to Rh(X)(CH 2 L), where L = tertiary phosphine) and the attack by external nucleophiles (e.g., methoxide, pyridine) on the Rh−CH 2 X moiety.…”