X-ray crystal-structure determinations

In the case of phenyllithium, it has been possible to demonstrate by NMR studies that the compound is tetrameric in 1 2 ether-cyclohexane but dimeric in 1 9 TMEDA-cyclohexane. X-ray crystal structure determinations have been done on both dimeric and tetrameric structures. A dimeric structure crystallizes from hexane containing TMEDA. This structure is shown in Fig. 7.1 A. A tetrameric structure incorporating four ether molecules forms from ether-hexane solution. This structure is shown in Fig. 7.IB. There is a good correspondence between the structures that crystallize and those indicated by the NMR studies. 

X-Ray crystal structure determinations of l-(aminocarbonyl)-3-methyl-4-methoxy-l//-pyrazol-5(2H)-one 107 (R = H) and l-(phenylaminocar-bonyl)-3-methyl-4-methoxy-l//-pyrazol-5(2H)-one 107 (R = Ph) demonstrated that both molecules exist in the crystal exclusively as NH-CO tautomers (97T5617). The tautomeric form similar to 104b is realized in the crystal of 4,4-dichloro-substituted pyrazolone 108 (93BSB735). 

An X-ray crystal-structure determination (370) revealed that mixed, nickel coordination exists in the trimeric complex, [Ni(S2CPh)2]3. The trimeric structure is similar to that found (371) in [Pd(PhCS2>]. The structure contains one molecule of type A linked centrosymmetrically through short Ni-S bridges to two molecules of type B, the three molecules being closely parallel (XXVII). Bonamico and co-workers (372)... 

Symmetrical cyanine dyes, because of the resonance shown in Figure 6.4 (in which the two contributing structures are exactly equivalent), are completely symmetrical molecules. X-ray crystal structure determinations and NMR spectroscopic analysis have demonstrated that the dyes are essentially planar and that the carbon-carbon bond lengths in the polymethine chain are uniform. The colour of cyanine dyes depends mainly on the nature of the terminal groups and on the length of the polymethine chain. The bathochromicity of the dyes is found to increase... 

Reactions of the Ir1 complexes (289) and (290) with H2 and subsequent reaction of the dihydride products with dimethyl acetylenedicarboxylate, Me02CC CC02Me (dma), give the Ir11 complexes (291), (292), (293), and (294), as shown in Reaction Scheme 26.482 The X-ray crystal-structure determination of (294) confirms the double insertion of the alkyne into each of the Ir—H bonds of (293). 

Technetium compounds with amine/thioether coordination are the cationic trans-dioxotechnetium(V) complexes [Tc02(N2S2)]+. The complex in which N2S2 is l,4-dithia-8,ll-diazacyclotetradecane was prepared via an exchange reaction of NBu4[TcOBr4] with the ligand and fully characterized by X-ray crystal structure determination [109,110]. The coordination around technetium... 

Zheng et al. treated potassium [l,2,4]diazaphospholides, obtained from the reaction of 3,5-disubstituted-[l,2,4]diazaphospholes with metallic potassium in THF, with [Cp RuCl]4 to afford [(T75-dp)RuCp ] type pseudoruthenocene complex (106) (Scheme 33). Sandwich structure with almost eclipsed orientation of two n-bonded ligands has been confirmed by X-ray crystal structure determination [110], Catalytic application of [(rf-dp)RuCp ] complexes in the Heck reaction has also been investigated [111]. 

The late stages of the synthesis (Scheme 1.17) proceeded with Wittig methylenation of ketone 144 with Ph3P=CH2 at 70 °C to furnish exocyclic alkene 145 in 77 % yield. Finally, the alcohol was installed via a Se02-mediated allylic hydroxylation [57] of the exocyclic alkene 145 to afford ( )-nominine (1) in 66 % and 7 1 dr. The structure of nominine (1) was verified via an X-ray crystal structure determination, thereby completing the racemic total synthesis of ( )-nominine (1). 

On reaction with MeMgCl, the lithium triazine Li(TF[F)2 N[C(Ph)=N]2 CBut(Bun) yields the methylmagnesio-dihydrotriazine 86 (Equation (18)). An X-ray crystal structure determination revealed that the compound closely resembled its lithio precursor the formal substitution of MeMg+ (Mg-C = 2.164(3) A) for Li+ did not produce the substantial structural differences often observed between isoleptic organolithium and organomagnesium systems.267... 

It has been several decades since oxo-centered triruthenium-carboxylate complexes with triangular cluster frameworks of Ru3(p3-0)(p-00CR)6 (R = alkyl or aryl) were first isolated [1,2]. In the early 1970s, the first oxo-centered triruthenium complex was structurally characterized by Cotton through X-ray crystal structural determination [3]. Since then, oxo-centered trinuclear ruthenium-carboxylate cluster complexes with general formula [Ru30(00CR)6(L)2L ]n+ (R = aryl or alkyl, L and... 

Vinylboronates are generally less reactive than vinylzirconocenes towards various electrophiles and hence selective reactions of the latter should be possible. It was found that selective cleavage of the carbon—zirconium bond in 45 by N-halosuccinimides provides (a-haloalkenyl)boronic esters 53 in excellent chemical yields and with complete re-gioselectivity (Scheme 7.17) [54], An X-ray crystal structure determination of 45 confirmed the configuration of the four-coordinate Zr complex, with two cyclopentadienyl rings, Cl, and C(sp2) as the four ligands (Fig. 7.5) [54,126]. 

An X-ray crystal structure determination of calciferol (vitamin D-2,71) showed that steric crowding in the s-cis diene system resulted in a twisted conformation with a dihedral angle of 53° [59], On irradiation with a mercury lamp, it was partially converted into ergosterol (72) and tachysterol (73) [60, 61]. When a solution of calciferol in light petroleum containing a trace of iodine was exposed to diffuse daylight, the vitamin was photoisomerized to (74) [62],... 

The long Cu-S(Met) bond (2.9 A) does not contribute to the EXAFS fit for PCu(II) under a variety of conditions, including studies on orientated single crystals at liquid He temperatures [38]. From fitting procedures reported the two Cu-N(His) bonds at 1.97 A are 0.1 A less and the Cu-S(Cys) distance 2.11 A (0.02 A smaller) than those obtained from the X-ray crystal structure determination [16]. 

Since isolable organocopper) 11) compounds do not apparently exist, it is rather surprising that oxidation of the cuprate CdI+[(CF3)2Cu ] (prepared in situ) with thiuram disulfide affords (CF3)2Cu "S2CNEt2 (see Eqn. 1 in Scheme 1.6), the first and so far only example of an organocopper compound with the copper atom in the trivalent oxidation state. The structure of this compound was unambiguously proven by an X-ray crystal structure determination (see Fig. 1.2) [37]. 

As mentioned above, one of the thermal decomposition pathways of alkylcopper compounds involves a j8-hydrogen elimination process, and so it is not surprising that the first well characterized alkylcopper compounds lacked such yS-hydrogens. Treatment of LiCH2SiMe3 with Cul afforded a tetrameric aggregate, the structure of which was unambiguously proven by an X-ray crystal structure determination (see Fig. I.IB in the previous section). This represented the first example of a well characterized alkylcopper compound [17]. 

More recently, several arylcopper compound syntheses that make use of a soluble form of a copper halide precursor, CuBr-DMS (DMS = dimethylsulfide) in DMS as the solvent have been reported. Some of these compounds, such as [Cu4(QH5)4(DMS)2] [61] and [Cu4(C6H4Me-2)4(DMS)2] [62], appeared to be DMS adducts and were fully characterized by X-ray crystal structure determination (see Fig. 1.7). It is interesting to note that these structures contain two- and three-coordinate copper atoms in trans positions. These structures may be envisaged as ion-pairs comprising Cu(Aryl)2 anions bound to Cu(DMS) cations through the Cipso atoms. 

---