Bridging hydroxo complex

A pyrolylnickel complex 21 also could activate water to afford a bridging hydroxo complex 22 accompanying cleavage of the Ni-carbon bond (Eq. 6.12) [20]. The hydride (hydroxo) species was not observed in the reaction mixture. 

ApoSOD, 45 186, 190 Apo VFe protein, 47 204 APS reductase, see Adenylylsulfate reductase Aqua-bridged hydroxo complexes acid-base equilibria, 32 110 of dihydroxo-bridged species, 32 114-115... 

The synthesis of bridging hydroxo complexes of platinum has been reported by Fakley and Pidcock (64). Treatment of bridging chloro complexes (e.g., 58) with aqueous potassium hydroxide, benzene, and a... 

It is interesting that Ir-OH exhibits stable catalysis (TON of >300 observed) and is not deactivated by the irreversible formation of bridging hydroxo species (assuming thermodynamic control) [29] that is common for metal hydroxo complexes. Our attempts at synthesis of these bridging hydroxo complexes have thus far been unsuccessful. Calculations show that the formation of a //-hydroxo bridged complex from two molecules of Ir-OH is not very favorable (AGrxn= -2 kcal/mol) and may serve to explain the catalytic stabihty of Ir-OH. 

Adventitious water is responsible for the formation of the dimeric hydroxo complex 31 obtained by reaction of AuCb with 1,4-dilithiotetraphenylbutadiene in ether solution [97[. The hydroxo-bridged complex [Au(C6H4N02-2)2( i-0H)[2 (32) was obtained either by reaction of Na[Au(C6H4N02-2)2(0Ph)2] with traces of water in CH2Cl2/n-hexane solution or by treatment of the dichloroaurated complex with NaOH [98[. The crystal structure of 32 2Et20 shows that it is a centrosymmetric... 

Treatment of the cyclometallated complexes [Au(N,N,C)Cl][PF6] [N,N,CH = 6-methylbenzyl- (a) or 6-(l,l-dimethylbenzyl)-2,2 -bipyridine (b)] [20] with KOH or Ag20 in aqueous media affords the hydroxo complexes [Au(N,N,C)(OH)][PF6] (36) in fairly good yields [45b, 101] these are air-stable white solids, quite soluble in water and in many organic solvents. When refluxed in anhydrous THF they condense to give the oxo-bridged complexes [Au2(N,N,C)2( J--0)] (37) (Equation 2.10 in Scheme 2.5) which, in turn, can be obtained by a different route [102] (see Section 3.2) the reaction can be reversed by refluxing the 0x0 complex in water. 

The hydroxo complexes [Au(6-Rbipy)(OH)2], postulated as intermediates in the formation of 44c-i, are not isolated nevertheless, in all the mass spectra (FAB conditions) a weak peak is found corresponding to these species. Unchanged 44c-i are quantitatively recovered from the reaction with aqueous solutions of HX (X = BF4 or PFfi) neither dihydroxo complexes similar to those observed in the vapor phase, nor hydroxo bridged dimers are obtained [25]. 

The binuclear Co(n) cryptate (monohydroxo bridged) was also found to combine reversibly with dioxygen yielding a doubly-bridged cascade complex containing both hydroxo and peroxo bridges within the cryptate structure. 

There has been a continuing discussion without resolutions of whether the aqua group acts as a (weak) bridge in the situations where the corresponding hydroxo complex reacts inner-sphere. 

---