Complexes of the Type M L

Table V summarizes the precursor complexes containing three or only one coordinated phenolato group. Octahedral complexes of the type [M(L,BuMet)-(Ph2acac)]+ or [M(L,BuMet)(Bu2acac)]+ (M = Cr111, Mnm, or Gam) display a reversible one-electron oxidation in the rather narrow potential range +0.24-0.51 V irrespective...

The divalent polyether antibiotics have revealed the existence of dimeric molecules as monomeric complexes in their interaction with alkali and alkaline earth cations. Lasolocid (145) forms complexes of the type M+L and these may be monomeric when formed and recovered from methanol, but dimeric when recrystallized from the non-polar carbon tetrachloride. The shortened ligand backbone relative to the monovalent polyethers does not allow complete shielding of the cation from the solvent, and so in non-polar solvents this is overcome by dimerization. If the salicylate and tetrahydropyran moieties present in (145) are referred to as the head and the tail of the molecule then two forms of dimerization may be envisaged head-to-tail and head-to-head . 

A variety of square planar complexes of the type M (l,2-diimine)(dithiolate) with M=Ni, Pd, and Pt are characterized by low-energy (dithiolate " 1,2-di-imine) LLCT transitions [7, 154, 158]. Such LLCT states may be luminescent (Fig.l0)[159],e.g.,... 

Singly substituted species M(CO)n iL have been investigated [49-51, 54, 55], Table 7.3 lists the calculated BDEs of the group-6 complexes of the type M(CO)5L (M = Cr, Mo, W) with various ligands L, whereas Table 7.4 contains the BDEs for the W-L and the W-CO bonds in W(CO)5L complexes. The latter values are given for the least bonded carbonyl ligand. Note that BDEs for other W(CO)5L complexes with certain particular classes of ligands are discussed in other sections of this chapter. 

There are two likely pathways for the replacement of chelates in complexes of the type M(C0)4(L2) by an incoming unidentate nucleophile, L,... 

The X-ray structure of 83 was in accord with the prediction of Scheme 4 in that the Si-Cl bond lies in the niobocene bisecting plane trans to the hydride and is elongated compared with classical complexes of the type [M(SiR2Cl)L ]. There was, however, no good reference system that would allow for the comparison of the Nb-Si bond lengths. The metal-silyl bond lengths are strongly affected by Bent s... 

Much of the chemistry of the vinylidene group was established with Group 8 complexes of the type [M(=C=CRR )(L )(P) Cp ]+ and several of the ubiquitous reactions of vinylidenes with 0-, S- and N-nudeophiles and with electrophiles have been mentioned above. 

Other anionic complexes of beryllium that have been detected are (NH4)2Be(N03)4,141 (NH4)2Be(NCS)4-MeCN and (NH4)2Be(NCS)3-MeCN.142 ESCA studies on beryllium and magnesium complexes of the type [M(NCS)4]2 and [M(CNS)3L] (L = DMF, py, MeCN) are consistent with N-bonding thiocyanate anions being present.142 The structure of K[Be(NH2)3] shows the beryllium to be in a trigonal planar unit.143... 

Cationic methylplatinum(II)-nitrile complexes of the type m is-PtMeL2(NCR)+X have been isolated by the reaction of //vms-PtMeClL2, where L = dimethylphenylphosphine or trimethyl-arsine, with an aryl nitrile and AgX, where X = BF4, PF. Use of pentafluorobenzonitrile and 2,3,5,6-tetrafluorotetraphthalonitrile in alcohol has led to the synthesis of a series of imino ether complexes. A mechanism for imino ether formation, involving nucleophilic attack by an alcohol at a coordinated nitrile, is suggested and the course of the reaction is shown to be dependent not only on the alcohol but also on the size of the anion used.110... 

Metal carbonyl complexes of the type M(CO)4L, where M = Cr, Mo, or W and L is the bidentate 2,7-dimethyl-l,8-naphthyridine, have recently been prepared by Hendricker and Reed.157... 

A range of compounds of the type M(L)I (where L = PC, or a substituted PC, and M = Ni, Co, Cu or Pt and 0 < x < 5) has been reported.90 All the compounds have room temperature conductivities much higher than the parent unoxidized compound. Studies reveal that for the system Ni(PC)Ix, when x < 113 is present, and when x> 1 another species in addition to I3 is present. Much further work needs to be done on these systems before they are fully understood. The importance of substituents on the PC ligand is shown by experiments on metal complexes in which the PC ligand contains four electron withdrawing substituents (e.g. Cl, N02 or S02H). No iodine uptake was observed and there was no increase in conductivity.90... 

Buckingham and Engelhardt200 have studied the hydrolysis of propionic anhydride in the presence of kinetically inert complexes of the type [M(NH3)5OH]n+. These reactions occur by nucleophilic attack of coordinated hydroxide on the anhydride (Scheme 32). For reactions of M-OHl" l,+ with propionic anhydride, the Bronsted plot of log kMOH versus the p.Ka of M—OH2k+ is a smooth curve if values for reaction with HzO and OH- are included. Although Icmoh for [(NH3)5CoOH]2+ (3 M-1 s-1) is about 103-fold less than fcoH. its reaction will compete favourably at neutral pH with base hydrolysis. Such effects are considered in more detail in Section 61.4.2.2.3. 

This approach, in which an arene appended to a coordinated donor atom replaces a labile ligand, is by far the most generally useful procedure and has been applied to the preparation of tethered arene complexes of Ti(IV), Cr(0), Mo(0), Mo(II), W(II), Ru(II), Rh(I), and Ir(I). The labile ligand itself is often an arene, as shown in Scheme lb, in which case the replacement is an intramolecular version of the intermolecular exchange between free and coordinated arenes, which has been studied for complexes of the type [M(CO)3(ri6-arene)] (M = Cr, Mo),26 31 [Ir(ri6-arene)(ri4-l,5-COD)]BF4,28 32 and [Ru(ri6-arene)(ri4-l,5-COD)]28 (COD = cyclooctadiene). 

The composition of the complexes above depends on the metal nature and its oxidation state. Thus, divalent copper, zinc, and cadmium form complexes of the type 811a (L = py, bipy, 1,10-phen m= 1, 2) [605], tetravalent tin forms chelates 811b (X — S [606], Se [607]). The electrochemical cleavage of the S — S bond is observed not only in ligands with aromatic bridge 810, but also in those with aliphatic one, for example (CH2) in 812 [608] ... 

Although the above discussion is centered on the synthesis of polymeric osmium and ruthenium complexes, the methods employed are also very successful in the preparation of mononuclear complexes. In this context, the preparation of ruthenium or osmium complexes which are suitable for the formation of self-assembled monolayers (see Section 4.3 above) can be prepared by using the same approach. Starting from the precursor [M(bpy)2Cl2], one chloride atom can be replaced to yield complexes of the type [M(bpy)2Cl L]+, where L is the surface active ligand. In the presence of water, species of the type [M(bpy)2(L)2]2+ are obtained. 

Photochemical oxidation of square-planar bis(l,2-dithiolene) complexes of Ni, Pd, and Pt is by no means limited to IPCT excitation. Photooxidation also occurs in halocarbon solvents. In 1982, two separate reports addressed the photochemistry of metal bis(l,2-dithiolene) complexes. Vogler and Kunkely (80) investigated complexes of the type M(S2C2R-2)2, where M = Ni, Pd, Pt,... 

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