Coordination complexes bridging diphosphines

Fig. 7. Structures of some possible Au(f) diphosphine complexes (1) bridged digold, (IT) annular, (III) tetrahedral, (IV) chelated 3-coordinate complex...

Carty AJ, Efraty A (1969) Coordination complexes of acetylene diphosphines. II. Diphosphine bridged palladium(II) and platinum(II) derivatives. Can J (Them 47 2573-2578... 

Catty AJ, Efraty A (1%9) Coordination complexes of acetylene diphosphines. I. diphosphine-bridged binuclear copper(l) and gold(I) complexes of bis(diphenylphosphino)acety lene. Inorg Chem 8 543-550... 

Although diphosphine disulfides of formula R2P(S)P(S)R2 take up a trans conformation in the solid state (see Section 5.2.3), upon coordination to a metal centre they can rearrange to adopt a cis conformation, hence facilitating bidentate chelation of the metal (e.g., Equation 78).117 In addition, a cis-bridging mode has also been proposed for these ligands in bi-metallic complexes.117... 

In closely related experiments it was shown that sp C—H activation takes place reversibly within the coordinahon sphere of the electron-rich Ir(I)-diphosphine complex 58 (Scheme 6.9) to form an alkyl-amino-hydrido derivative 57 reminiscent of the CCM intermediate 24 the solid-state structure of 57 is shown in Figure 6.13 [40]. It appears that C—H activation only takes place after coordination of the amine function to the Ir(I) center (complex 58, NMR characterized). Amine coordination allows to break the chloro bridge of 59 and to augment the electron density of the metal center, thus favoring oxidative addihon of the C—H bond. Most importantly, the microscopic reverse of this C—H activation process (i.e. C—H reductive elimination) models the final step of the CCM cycle (see Scheme 6.1) indeed, the reaction of Scheme 6.10 is cleanly reversible at 373 K. 

It is also possible for the anion to coordinate in similar complexes to give three-coordinate gold(I) centres in (41)371-373 in which the diphosphines bridge between gold(I) centres, or in (39) and (42) in which the diphosphines chelate.356,374 In the binuclear complex (41a) the AuAu separation is only 296 pm.371... 

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