Stereochemie der Metall‐Metall‐Bindung. Strukturvergleiche von isoelektronischen zweikernigen Cyclopentadienylmetallcarbonylen

Abstract

Die Kristallstrukturen der neuen Komplexe Cp(CO)3CrNi(CO)Cp (4) und (CO)5MnNi(CO)Cp (5) wurden ermittelt, diejenige von [Cp(CO)Ni], (3) wurde neu vermessen. In diesen Komplexen bestimmt wie in ihren isoelektronischen Partnern [Cp(C0)3Cr]2 (l), [Cp(CO),Fe], (2) und Cp(CO)2FeCo(C0)4 (6) hauptsachlich die intramolekulare Packung der Liganden die Molekulgeometrie. Die Metallatome befinden sich nicht in regelmafiigen Koordinationspolyedern, und die Metall-Metall-Bindurigen nehmen keinen typischen Platz in den Koordinationsspharen ein. Die Ligandabstofiungen verursachen in der Reihe 1, 2, 3 die ungewohnlich grofie Variation der Melall-Metall-Abstande und die verschiedene Faltung der Molekulgeruste entlang der M -M-Verbindungslinie. Sie lassen es zu, da8 das im engeren Sinne isoelektronische Komplexpaar 2/4nahezu isoster ist. Beim analogen Komplexpaar 5/6 ist die Strukturverwandtschaft weniger offensichtlich, da sich 6 als cis-und 5 als trans-Isomeres klassifizieren lafit. Stereochemistry of the Metal-Metal Bond Structural Comparisons of Isoelectronic Dinuclear Cyclopentadienyl Metal CarbonylsThe crystal structures of the new complexes Cp(CO),CrNi(CO)Cp (4) and (CO)SMnNi(CO)Cp (5) were obtained, that of [Cp(CO)Ni], (3) was redetermined. In these complexes like in their isoelectronic counterparts [Cp(CO),Cr], (l), [CP(CO)~F~], (2), and Cp(CO),FeCo(CO), (6) the molecular geometry is determined predominantly by the intramolecular packing of ligands. The metal atoms are not in the centres of regular coordination polyhedra, and the metal-metal bonds do not occupy typical positions in the coordination spheres. In the series 1,2,3, the ligand repulsions cause the unusually large variation of the metal-metal distances and the different folding of the molecular frames along the M -M connection. They allow the complex pair 2/4 which is isoelectronic in the narrower sense to be nearly isosteric. For the analogous complex pair 5 / 6 the structural similarity is less obvious since 6 can be classified as a cis and 5 as a trans isomer. Th. Madach, K . Fischer und H. VahrenkampJahrg. 113

Geometric and Electronic Structure Analysis of the Three-Membered Electron-Transfer Series [(μ-CNR)2[CpCo]2]n (n = 0, 1–, 2−) and Its Relevance to the Classical Bridging-Carbonyl System

“…1 H NMR (400.1 MHz, C 6 D 6 , 20 °C): δ = 6.97 (s, 8H, m-Mes), 6.86 (m, 3H, J = 4 Hz m/p-Ph), 4.76 (s, 10H, Cp-H), 2.28 (s, 12H, p-CH 3 ), 2.18 (s, 24H, p-CH 3 ) ppm. 13 Synthesis of [CpNi(CNAr Tripp2 )] 2 (7). To a forest green C 6 H 6 solution (5 mL) of Cp 2 Ni (0.150 g, 0.794 mmol, 1 equiv) was added a C 6 H 6 solution of CNAr Tripp2 (0.403 g, 0.794 mmol, 1 equiv, 5 mL).…”

“…The resultant mixture was frozen, and all volatiles were removed via lyophilization. The resultant dark red powder was recrystallized from a 6:1 n-pentane/toluene mixture at −40 °C overnight to yield [CpNi(CNAr Tripp2 )] 2 (7) as dark red crystals. Yield 0.155 g, 0.123 mmol, 31%.…”

“…The dimeric cyclopentadienyl complexes [(μ‑EO) 2 ­[CpM] 2 ] n (E = C, N; M = Fe, Co, Ni; n = 0, 1−) are well known species that provided early tests for metal–metal multiple bonding and mixed valency in organometallic systems. − However, the degree of M–M bond multiplicity in these dimers, as well as the fundamental question as to whether M–M bonds are present at all, has remained contentious. − The central issue in this debate has stemmed from the discrepancy between classical electron-counting formalisms and the crystallographic and/or theoretically determined structural features of the (μ‑EO) 2 M 2 core. , These structural features (Scheme ), which include the M–M separations ( d ), (μ‑EO) 2 M 2 core puckering (θ), and Cp-ring slippage ( s ), do not track straightforwardly with the formal d n combination of the two metal centers (i.e., d 8 –d 8 , d 9 –d 8 , d 9 –d 9 ). In addition, the well-recognized and substantial contribution that the bridging ligands make to the electronic structure has also compounded the difficulty in determining the extent of M–M bonding interactions of these dimers. , …”

“…While significant synthetic, spectroscopic, and theoretical attention has been given to [(μ‑EO) 2 ­[CpM] 2 ] n dimers, − it has been noted previously that synthetic access to a homologous series of d 8 –d 8 , d 8 –d 9 , and d 9 –d 9 partners has been the main limitation of a full, systematic investigation into this class of complexes. , For example, the neutral bridging carbonyl complex (μ‑CO) 2 ­[CpCo] 2 and its radical anion [(μ‑CO) 2 ­[CpCo] 2 ] − , which function as d 8 –d 8 and d 8 –d 9 pairs, respectively, have been well studied. − However, the corresponding dianion [(μ‑CO) 2 ­[CpCo] 2 ] 2– , which represents the d 9 –d 9 combination, has remained elusive toward isolation. , To combat this synthetic limitation, the neutral dinitrosyl dimer [(μ‑NO) 2 ­[CpCo] 2 ], has served as a surrogate for the d 9 –d 9 system. ,,,, However, the differing orbital energies attendant between CO and NO can dramatically affect the energetics of the d-orbital manifold, , thus rendering this comparison imprecise for the goal of elucidating M–M bond multiplicity. ,, …”

Allylnickel(II) and Allylpalladium(II) Derivatives of [(2-(Diphenylphosphino)ethyl)cyclopentadienyl]tricarbonylmetalates: Reactions with Free Radicals

“…The Cr-Ni bonds of 1 (2.6182(5) A ˚), 4 (2.6110(8) A ˚), and 7 (2.6283(3) A ˚) are similar to that of Cr{Ni(η 5 -Cp)(CO)}(η 5 -Cp)(CO) 3 (2.641(3) A ˚). 28 The M 00 -Ni (M 00 =Mo, W) bonds of 2, 3, 5, 6, 8, and 9 range from 2.7077(8) A ˚(2) to 2.7478(4) A ˚( 6 1.934(5)-2.063(6) A ˚). 29 The Cr-Pd separation in 10 (2.7561(6) A ˚) is statistically identical to analogous lengths in diastereomers of Cr{Pd(η 3 -C 3 H 5 )}(CO) 3 (μ-η 6 :η 1 -PhHC(C 6 H 5 )) (16, Figure 5) (2.776(1), 2.770(1) A ˚).…”