Heteroleptic structures

Scheme 3 shows the details of the synthetic strategy adopted for the preparation of heteroleptic cis- and trans-complexes. Reaction of dichloro(p-cymene)ruthenium(II) dimer in ethanol solution at reflux temperature with 4,4,-dicarboxy-2.2 -bipyridine (L) resulted the pure mononuclear complex [Ru(cymene)ClL]Cl. In this step, the coordination of substituted bipyridine ligand to the ruthenium center takes place with cleavage of the doubly chloride-bridged structure of the dimeric starting material. The presence of three pyridine proton environments in the NMR spectrum is consistent with the symmetry seen in the solid-state crystal structure (Figure 24). 

Although the existence and structures of tetraorganozincates in the solid state are now well established, the reactivity patterns of these compounds in organic synthesis are still largely unknown. Homoleptic and heteroleptic tetrasubstituted dianionic zincates of the type [ZnR3X], X = Me, CN, SCN, were prepared as shown in Scheme 58... 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

A heteroleptic zirconium sandwich complex in which Zr links octaethylporphyrazine (28) and the structurally analogous octa-ethylporphyrin has also been reported. To spectroscopically study the... 

Structural Analysis. The crystal structures of the homoleptic Zr(TV) sandwich Zr[pz(5 -Et)8], and heteroleptic sandwich 30 (33) are similar to the structure reported for the analogous homoleptic porphyrin (73). 

Interestingly, the structural parameters for the individual pz and porphyrin subunits of the mixed sandwich complex are indistinguishable. Selected bond lengths and angles for sandwich compounds (29), the heteroleptic system (30), and the homoporphyrin analogue are listed in Table VI (33). 

As a further confirmation of the extended redox aptitude of polypyridine ligands, Figure 15 shows the cyclic voltammetric behaviour of the heteroleptic chromium(III) complex with 2,2/-6/,2"-6//,2"/-quaterpyr-idine (qpy), together with its molecular structure.28... 

Organic moieties containing potentially coordinating substituents are largely responsible for the diversity of structures observed in heteroleptic organocopper compounds. The structures observed in compounds containing one of the ligands depicted in Fig. 1.14 demonstrate that important roles are played not only by... 

An interesting feature of these compounds is that, upon thermolysis in benzene at 80 °C, the unsymmetrical C-C coupling product 2-Me2NC6H4C=CR is formed exclusively. The selectivity of this reaction is probably directly related to the structural features of this heteroleptic aggregate [89]. 

Fig. 1.28. Structures of heteroleptic cuprates CuLiMe(t-Bu2P)-(THF)3 (A) and [Cu4Mes4] [Mg(SC6H4CH(Me)NMe2-2)2l2 (B) in the solid state.

The reaction between equimolar quantities of LiCH(SiMe3)2 and CuBr in the presence of 12-crown-4 afforded [Cu(CH(SiMe3)2)Br][Li(12-crown-4)2], the first example of an ionic mononuclear heteroleptic cuprate [121] for which the structure was established by X-ray crystal structure determination (Fig. 1.31C). 

Comparisons between the electronic structures (using a ZINDO analysis) of [Ru(bpy)3] " and [Ru(bpy)(NH3)4], and between related pairs of compounds where bpy is replaced by 2,2 -bipyrazine or 1,2-benzoquinonediimine, show that bpy is unable to accept extra electron density from the metal center whereas the opposite is true for 1,2-benzoquinonediimine. The acceptor properties of the 2,2 -bipyrazine ligand fall between those of bpy and 1,2-benzoquinonediimine. Using the Fenske-Hall method, the electronic structures of [Ru(bpy)3 (ppy) ] "A (Hppy = 2-phenylpyridine) have been investigated. The coordinated ppy is a C,A-donor. The electronic structures of the heteroleptic complexes exhibit a separation of the Ru—C and Ru—N f7-bonding character. It is proposed that the observed preference for cis- over trans- and for fac- over nrer-isomers may arise from the enhanced cr-donating ability of the C atom when it is trans to an N rather than C-donor. ... 

---