Metal single-bonded complexes

Na[MeGa(pz)g] gives the metal-metal single bonded complex... 

Bullitt, J. G. Cotton, F. A. (1971) The structure of a dinuclear complex of osmium(I) with a metal-to-metal single bond bis-(/i-acetatojhexacarbonyldiosmium, Inorg. Chim. Acta. 5, 406-412. 

In all three complexes the Si-metal bond is short (Si—Fe = 219, Si—Ni = 221, Si—Cr = 228 pm). These distances are about 10 pm less than for typical Si-metal single bonds, consistent with partial back-bonding from the metal d-orbitals to the p-orbital on silicon. Reactions of 59 to form silylene-metal complexes appear to be general, and many more examples are likely to be prepared in the future, for this and other stable silylenes. 

TABLE 7. X-ray structural data of transition metal germanium single bond complexes... 

The product retains the Rh=Rh double bond in what is really a snbstitution of CO by CH2. Insertion of CH2 into a metal metal single bond is seen in the synthesis of the platinum A-frame complex shown in eqnation (39), a rare example of a bridging methylene complex withont an M M bond (stiucture of type (12)). 

The reaction of the dinuclear Rh(I) acetylacetonate carbene derivatives 96 with tertiary phosphines gives the mixed 0- and - -2-valent compound 97 (equation 64), a rare combination of two atoms of the same metal in different oxidation states. Such complexes, containing a d -Rh(O) and a d -Rh(II) metal centre, are diamagnetic and are characterized by a metal-metal single bond. 

In addition, metal-metal bonds must be counted. A metal-metal single bond counts as one electron per metal, a double bond counts as two electrons per metal, and so forth. For example, in the dimeric complex (CO)5Mn—MnfCOfs the electron count per manganese atom is (by either method) ... 

The heavy group VIII metals generally form tf , tf , or d ° mononuclear complexes with four- or six-coordinate geometry. Formation of metal-metal bonds frequently involves oxidation or reduction processes that yield a metal-metal single bond rather than multiple bonds, which are rare for these metals. This section discusses the steps in forming metal-metal bonds. Unusual reactivity of the metal-metal bonds is noted, but substitution reactions, which can give new complexes also containing metal-metal bonds, are not considered. Several reviews are available... 

The reactions of alkynes and alkenes with metal-metal multiple bonds in dinuclear complexs have important catalytic implications, but less attention is paid to their insertions into metal-metal single bonds. A 1965 publication comprehensively reviewing insertions of compounds of metals and metalloids involving unsaturated substrates lists insertions into metal-metal bonds prior to 1965. 

Complex 177 contains both MoVI and Mov ions, with the latter linked in pairs by metal-metal single bonds. Compound 178 involves a single-valent mo-lybdenum(VI) octamolybdenum species and is photosensitive. 

In dinuclear complexes containing a metal-metal single bond, the major consequence of irradiation is homolytic cleavage to form reactive metal-carbonyl radicals. Many simple substitutions can be explained by a mechanism involving thermal substitution of these radicals. This mechanism is especially helpful in explaining the formation of a disubstituted product ... 

This reaction is noteworthy in that multielectron transfer occurs without a change in stoichiometry of the redox active unit. Moreover, a metal-metal single bond is cleaved and large structural deformations — expansion and contraction of the M- -M and -M- angles by ca. 30° and an increase of >1.0 A in the M-M distance — occur within the intact M2 2 core as the complexes pass fi om the M(I)2 state to the M(0)2 state. These structural changes, which are illustrated in Figure 1, are presumed to provide the driving force for coincident two-electron transfer. 

As a matter of classification, these single bond complexes are divided into three groups according to the number of electrons formally donated by the borane ligand to the metal. The zero-electron donor (or electron pair acceptor) complex is exemplified by the compound Na[(OC)sMn BH3] (J), the one-electron donor by the compound l,2-(CH3)2-3-[(C5H5)Fe(CO)2]-BioC2H9 (2), and the two-electron donor by the compound (CH3)4N[7,8-B9H,oCHPCr(CO)5] (3). 

Wayland has synthesized Rh(OEP)In(OEP) by the reaction of (Na)[Rh(OEP)] with In(OEP)Cl This nucleophilic substitution of a metallate anion on a chloroindium(III) porphyrin is analogous to that reported for the synthesis of single bonded complexes containing one porphyrin unit The similar morphology of the NMR spectra for Rh(OEP)In(OEP) and [Rh(OEP)]2 suggests the existence of a metal-metal bond and this is confirmed by an X-ray study. Figure 23 shows the molecular structure of Rh(OEP)In(OEP) which consists of two face to face porphyrin units bound together via a Rh-In bond. 

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