Ethylene, silene, and disilene coordinate bonds with platinum(0) and platinum(II). An ab initio MO/MP4 and SD-CI study

Abstract

clearly indicate that the extra peaks originate from coordinated citrates and that the citrates are released to be averaged on the N M R time scale, when a sufficient amount of citrate (cit:Bi > 1:l) is present in the system. In fact, for the all other bismuth citrate compounds (1, Za, Zb, 3a, and 5) whose citrate:bismuth ratios are higher than 1 .O, all citrates average on the N M R time scale under low-concentration conditions, as mentioned above.According to the elemental analyses, 4a and 4b seem to contain [Bi-O(H)-Bi], units. The hydrolysis of Bi(II1) has been extensively studied and the predominance of several hexanuclear species, such as [ Bi604(0H)4]6+, in acidic solutions is well established.29,30 If the presence of such hexanuclear species is assumed for the solutions of 4a and 4b, then the behavior can be explained well. Since the hexanuclear unit decomposes in basic conditions, the "isolated" bismuth ions will be able to react with citrates, which exchange rapidly on the N M R time scale just like the other bismuth citrate compounds. An excess of citrate may coordinate with such a unit, so as to weaken and destroy the Bi-O bonds that are frameworks in a hexanuclear cluster. Although the structure determination of compound 4 as a solid has been attempted, this was unsuccessful so far, due to the poor quality of the crystals. Concluding RemarksIn this investigation, five types of solid compounds were synthesized by varying the Bi:H4cit:KOH:NH40H ratio. In the case of two compounds, i.e. 1 and 5, a 3-D structure could be determined by using X-ray diffraction on single crystals. For the citrate anion, whether in triionized or tetraionized form, tridentate chelation to Bi(II1) is evident. Only in the case of compound 4,As the citrate:bismuth ratio increases, the pH* value increases. Resultant pH* values for each citrate:bismuth ratio are as follows: pH* 6.96 for cit:Bi = 2:3 (without addition of free citrate), pH* 7.18 for 3:3, pH* 7.25 for 4:3, pH* 7.29 for 53, and pH* 7.31 for 6:3. (29) Baes, C. F., Mesmer, L. G., Eds. The Hydrolysis ofCarions; Wiley: New York, 1976. (30) Sundvall, B. Inorg. Chem. 1983,22, 1906 and references cited therein. (31) Weast, R. C. Handbook of Chemistry and Physics, 66th ed.; CRC Press, Inc.: Boca Raton, FL, 1986. (32) For example, a type 1 compound was obtained by concentrating the filtrate from which 3b was removed. When methanol vapor was diffused into the filtrate from which 2b was removed, type 4 was obtained.prepared with a small excess of citrate, are not all Bi ions tridentately chelated by citrate (ratio Bi:citrate = 3:2), and a cluster structure, such as [Bi604(oH)4(H~it)4]b, appears likely.To the best of our knowledge, the rapid ligand exchange of citrates is unprecedented for bismuth. On the other hand, in solutions with high concentration that are attained only under basic conditions, citrates coordinate to bismuth rigidly, to yield oligomeric or polymeric units. Exceptionally, compounds 4a and 4b show separate signals for free and coordinated citrates in their 'H ...

Bonding and structure of disilenes and related unsaturated group-14 element compounds

“…Among isolated mononuclear η 2 -disilene transition metal complexes 66a – 66c , 64 ) 67a – 67b , 64b) ) and 68a – 68b 65 ) (Chart 9 ), only the structure of tungsten complex 68a 65a) ) with a character of metallacycle had been determined by X-ray crystallography. The structural issue of the disilene-metal complexes were first discussed theoretically by Sakaki et al 66 ) and Gordon et al . 67 ) The ab initio MO calculations for (disilene)platinum complex 69a show that 69a features a large bent-back angle (α = ca.…”

“…25°), elongated Si-Si bond (Δ d = 0.124 Å) and small Si-Si stretching force constant (3.08 mdyn Å −1 for disilene, while 2.63 mdyn Å −1 for 69a ), and hence, 69a is characterized as a metallacycle. 66 )…”

A Combined Gas‐Phase Photoelectron Spectroscopic and Theoretical Study of Zeise’s Anion and Its Bromine and Iodine Analogues

“…[7][8][9] These findings can be qualitatively explained by the DCD bonding model, [3,4] and have been essentially confirmed by earlier molecular orbital calculations [13,14] and related theoretical studies. [15][16][17][18][19][20] Besides being a historically key species in the field of organometallic chemistry in defining new chemical concepts (such as hapticity) and modes of chemical bonding, Zeises salt and its dimer have also been found to be effective in many important catalytic processes, [21][22][23] as well as being used as versatile chiral derivatizing agents in asymmetric synthesis. [24,25] The Br analogue of Zeises salt is an important intermediate and was shown to activate the hydroamination of ethylene.…”

Synthesis and Structures of Zeise‐type Complexes with Vinylsilane Ligands and Quantum Chemical Analysis of the Platinum–Vinylsilane Bonding

“…In general, the calculated and experimentally found structures are in a good agreement. The slightly shorter PtϪCl bonds trans to the olefin ligands over those cis to the olefin ligands (∆ 0.003Ϫ0.014 Å ) can be rationalized in terms of the trans influence olefin > Cl Ϫ [23] and antibonding Pt(d π )ϪCl(p π ) interactions [24]. Whereas the ethylene ligand in 8c was found to be perpendicular to the complex plane (exp.…”

“…The bond dissociation energies D e of the olefin ligands in the complexes 4c؊6c and 8c [ [24,26]. The partitioning of the bond dissociation energy D e into a preparation term (∆E prep ) and an instantaneous interaction term (∆E int ) (see Ref.…”