Heteroleptic

Hydroc rbylComplexes. Stable homoleptic and heteroleptic thorium hydrocarbyl complexes have been synthesized. Two common homoleptic species are [Li-TMEDA]2 Th(CH2). ] [92366-18-2] (19), where TMEDA = tetramethyl ethylenediarnine, and Th(CH2CgH ) [54008-63-8] (20). 

Hydrocarbyl Complexes. Stable homoleptic and heteroleptic uranium hydrocarbyl complexes have been synthesized. Unlike the thorium analogues, uranium alkyl complexes are generally thermally unstable due to P-hydride elimination or reductive elimination processes. A rare example of a homoleptic uranium complex is U(CH(Si(CH2)3)2)3, the first stable U(I11) homoleptic complex to have been isolated. A stmctural study indicated a triganol... 

Heteroleptic complexes of uranium can be stabilized by the presence of the ancillary ligands however, the chemistry is dominated by methyl and benzyl ligands. Examples of these materials include UR4(dmpe) (R = alkyl, benzyl) and U(benzyl)4MgCl2. The former compounds coordinate "soft" chelating phosphine ligands, a rarity for the hard U(IV) atom. 

Another class of heteroleptic alkyl complexes contains TT-donating ancillary ligands such as RU[N(Si(CH2)3)2]3 (R = 4)- The hydride... 

A number of general features in Table 1-3 is apparent. Complexes may be cationic, neutral or anionic. Ligands may be simple monatomic ions, or larger molecules or ions. Many ligands are found as related neutral and anionic species (for example, water, hydroxide and oxide). Complexes may contain all of the same type of ligand, in which case they are termed homoleptic, or they may contain a variety of ligand types, whereby they are described as heteroleptic. Some ligands such as nitrite or thiocyanate can coordinate to a metal ion in more than one way. This is described as ambidentate behaviour. In such cases, we commonly indicate... 

Metathetical reactions between NbCl4(THF)2, NbCls, TaCls, [(Et2N)2TaCl3]2, or (R2N)3Ta(=NBu (R = Me, Et) with various amounts of lithium amidinates have been employed to synthesize the corresponding heteroleptic niobium and tantalum amidinate complexes. The products were investigated as potential precursors to metal nitrides (cf. Section VI) Carbodiimide insertion routes... 

This review deals with the chemistry and coordination complexes of isoelectronic analogues of common oxo-anions of phosphorus such as PO3, POl", RPOl" and R2POy. The article begins with a discussion of homoleptic systems in which all of the 0x0 ligands are replaced by imido (NR) groups. This is followed by an account of heteroleptic phosphorus-centered anions, including [RN(E)P(/<-NR )2P(E)NR]2-, [EP(NR)3]3-, [RP(E)(NR)2] and [R2P(E)(NR )] (E=0,S, Se, Te). The emphasis is on the wide variety of coordination modes exhibited by these poly-dentate ligands, which have both hard (NR) and soft (S, Se or Te) centers. Possible applications of their metal complexes include new catalytic systems, coordination polymers with unique properties, and novel porous materials. 

Tris(imido)phosphonates [R P(NR)3] and bis(imido)phosphinates [R 2P(NR)2] are not, strictly speaking, homoleptic anions. In this article, however, homoleptic refers to anions that contain only imido (NR) ligands, in addition to the H or R substituent directly attached to phosphorus (if any), whereas the term heteroleptic is used for anions that involve both imido and 0x0 (or chalcogenido) ligands. 

The chemistry of homoleptic polyimido and heteroleptic imido-oxo- or -chalcogenido anions of phosphorus is described in chapter 6 (T. Chivers). Emphasis is placed on the versatile coordination behavior of these multident-date hgands, which have both hard (NR) and soft (S, Se, Te) centers. 

Properties of nickel poly(pyrazol-l-yl)borate complexes such as solubility, coordination geometry, etc., can be controlled by appropriate substituent groups on the pyrazol rings, in particular in the 3- and 5-positions. Typical complexes are those of octahedral C symmetry (192)°02-604 and tetrahedral species (193). In the former case, two different tris(pyrazolyl)borate ligands may be involved to give heteroleptic compounds.602,603 Substituents in the 5-position mainly provide protection of the BH group. Only few representative examples are discussed here. 

Homo- and heteroleptic complexes of Cd alone and of Cd and Hg with the ligand dicyanamide (dca) N(CN)2-, homologous to cyanamide NCN2-, have been studied in various solvents (formation constants of the complexes [M(dca) ](" 2> (M = Cd, Hg l < n < 4)), with the result that the complexes of Hg are more stable than those of Cd. Otherwise, obviously no studies on the isolated compounds M(dca)2 or on homoleptic complexes derived therefrom have been published. 

The low efficiencies could be due to lack of intimate contact (interface) between the sensitizer (which is hydrophilic) and the spirobifluorene (which is hydrophobic). Moreover, the surface charge also plays a significant role in the regeneration of the dye by the electrolyte.98 In an effort to reduce the charge of the sensitizer and improve the interfacial properties between the surface-bound sensitizer and the spirobifluorene hole-carrier, amphiphilic heteroleptic ruthenium(II) complexes ((48)-(53)) have been used as sensitizers. These complexes show excellent stability and good interfacial properties with hole-transport materials, resulting in improved efficiencies for the solar cells. 

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