Two-electron ligands

The ruthenium analogue of 47 Ru(ri5-C5Ph5)(CO)2Br (48) is also available, when Fe(CO)5 is replaced by Ru3(CO)12 [68]. A wide range of substitution products were obtained through replacement of both carbonyl and bromide ligand against two-electron ligands L such as phosphines, phosphites, and ethylene. Electrochemistry of these derivatives were studied in some detail. 

The electrochemical behavior of an aqueous/ethanol solution of [Ir(sat)2]Cl, satH = salicylaldehyde thiosemicarbazone (235), has been studied on mercury. A two-electron, ligand-based reduction at —1.09 V vs. SCE (independent of pH) is observed at fast scan rates.406... 

Not included in the present review is the fascinating new chemistry which results from reaction between diazo compounds and low-valent transition-metal complexes bearing easily displaceable two-electron ligands as well as with metal-metal multiple bonds and metal hydrides whereby a variety of novel organometallic molecules could be obtained. This field has been covered, in accord with its rapid development, by successive reviews of Hermann 19 22) and Atbini23). 

Nitrosonium complexes 20a-d of l-R-2-methylacenaphthylenes 21a-d (Scheme 15) can be considered as complexes with two-electron ligands, as unlike complexes of other polycyclic aromatic compounds (8, 52), nitrosonium... 

Form A is a transition metal hydride while in form B the silicon hydride behaves as a two electron ligand. The electrons donated by the ligand to the transition metal happen to be a bonding pair in H-SiRj instead of a non-bonding pair in... 

However, deinsertion involving two electron ligands is not a general reaction for all the hydride complexes. Indeed, the iron complex (CO)4Fe(H)SiPh3 undergoes CO replacement rather than deinsertion ... 

Ligand (233) contains two 1,2-phenylenediamine domains that can be independently oxidized, and this is observed in the complex [(NH3)4Ru(/i-233)Ru(NH3)4] " " which undergoes two, two-electron ligand-oxidation processes further oxidation generates Ru -containing... 

The presence of multiple donor sites enables cyclophosphines cyclo-(PR) n = 3-6) to function as versatile two-electron ligands in mono- di- or trinuclear metal complexes as discussed in Section 7.1.1 (see structures 7.1-7.3) in some case the reaction of cyclo-(PR)5 with transition metal complexes results in P-P bond activation, which may occur either with retention or fragmentation of the oligophosphine (for examples, see structures 7.4-7.5). ... 

The electrons courted for the metal atom in each of these complexes are those in its valence s and it orbitals. Metals having odd numbers of electrons obviously cannot satisFy the 18-electron rule by simple addition of CO (or other two-electron) ligands because the resulting moiety will necessarily also have an odd number of electrons. For example, Mn(CO)t and Co(CO)4are both 17-electron species and, consistent with prediction, do not exist as stable molecules. However, their corresponding anions, [MrtCOIjJ- and [Co CO>4] , are stable species and conform to the 18-electron rule. 

The acetonitrile ligand in Rh6(CO)i5NCMe is very labile and can be readily substituted by other two-electron ligands.5 8... 

Electron counting in these electron-deficient systems is slightly different than in electron-precise hydrides. As noted by Green,8 canonical forms can be written in which the hydrogen is treated normally vis-a-vis one metal and the M—H bond is treated as a two-electron ligand to the second... 

The possibility of coordination of a two-electron ligand, in addition to arene, to the ruthenium or osmium atom provides a route to mixed metal or cluster compounds. Cocondensation of arene with ruthenium or osmium vapors has recently allowed access to new types of arene metal complexes and clusters. In addition, arene ruthenium and osmium appear to be useful and specific catalyst precursors, apart from classic hydrogenation, for carbon-hydrogen bond activation and activation of alkynes such compounds may become valuable reagents for organic syntheses. 

Sixteen-electron ruthenium(O) species of type (rj6-arene)(L)Ru(0) and containing two-electron ligands are probable intermediates for C—H bond activation and formation of metallacyclic complexes (Section II,A,3,c). A variety of 18-electron complexes of general formula (arene)(L1)(L2)Ru(0) have been prepared by H. Werner and co-workers either by deprotonation of hydride ruthenium(II) complexes or by reduction of cations RuX(L)2-(arene)+. Some of these Ru(0) complexes have already been discussed with the formation of alkyl or hydridoruthenium complexes (Sections... 

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