Organometallics the metal d orbitals. Linear combinations of la, and 3bg can be ma$: in order to emphasize net interactions. Orbitals la,, 4b,, 5ag, and the linear combinations of la, and 3bg are shown in Figure 5. Of course la, and 3bg can be regenerated by adding or subtracting, respectively, the linear combinations illustrated in Figure 5.According to the 18-electron rule, the formal metalmetal bond orders of the dicarbonyl-and dinitrosyl-bridged dimers are 2.0 and 1.0, respectively. In the dicarbonylbridged dimers all orbitals shown in Figure 5 are filled except 5ag, the LUMO. The two metal-metal bonds are represented by la, and 4b,. These are 4c-2e bonds and contain substantial amounts of CpM-EO bonding. The linear combinations of la, and 3b are exclusively CpM-EO bonding. In dinitrosyl-bridged dimers all orbitals are filled, including 5%. The out-of-plane a metal-metal bond in 4b, is more than cancelled by the out-of-plane x* metal-metal antibond in 5ag. Therefore, in dinitrosyl-1988Therefore, in dinitrosyl- , 7, 1930Therefore, in dinitrosyl- -1938 bridged dimers the only net metal-metal bonding interaction is the in-plane u bond in 1%. The description given above neglects the le, and lal fragment orbitals and this tp,-like set is usually believed not to contribute to metalmetal bonding, but as shown in Table VI and in Figure 4, the lal fragment orbitals do contribute some additional metal-metal bonding because the bonding in the 3% is not completely cancelled by their antibonding counterpart, 3b,.A series of rhenium(II1)-oxo-alkoxide-bis(acety1ene) complexes of the form Re(0)(OR)(R'Cd!R')z have been prepared by reaction of the iodide derivatives R~(O)I(R'CECR')~ with thallium alkoxides. An X-ray crystal structure of the phenoxide complex 7a shows the pseudotetrahedral coordination geometry typical of Re(0)X(RC=CR)z compounds, with a short rhenium-oxo bond of 1.712 (13) A and a longer Re-OPh distance of 1.966 (14) A. The alkoxide complexes decompose in solution at less than 100 "C by a number of pathways including @-hydrogen elimination. The complexes react rapidly with protic reagents such as alcohols, water, amines, acids, etc. with displacement of alcohol. Reactions of the tert-butoxide complex with ammonia or methylamine yield the corresponding amide complexes, and H2S gives the hydrosulfide species. Many of these ligand exchange reactions give equilibrium mixtures, indicating that the Re-X bond strengths in general parallel H-X bond strengths. The methylamide complex is fluxional on the NMR time scale, with a ground state that places the methyl group pointing at one of the acetylene ligands. The phenoxide ligand in the X-ray structure is approximately in the same sterically encumbered orientation. This orientation is preferred because it favors a-bonding and minimizes n-antibonding interactions of the a-donor orbital of the amide or phenoxide ligand. The ethoxide complex readily inserts carbon monoxide
:A stirred solution of 1 (180 mg, 0.37 mmol) in CH2ClZ (17 mL) was treated at 20°C with 0.23 mL (283 mg, 1.27 mmol) of CF3SOlSiMe, (the deep-red solution turned pale red within 1 min). After three hours' stirring, all volatile components were removed under high vacuum at 20°C. The oily, brown residue became solid after repeated washing with n-pentane and drying in a 191. Angew. Chem. Inr. Ed. Engl. 2711988) No. 11 0 VCH VerlagsgeseNscha/l mbH. 0-6940 Weinheim, 1988
wolframatkomplexes mit Cyclooctan (Reaktionen 16 und 18-2 1). Dies sind die bei weitem hochsten Quantenausbeuten fur eine photochemische Reaktion auf Polyoxometallatbasis. Da Reaktion (e) endotherm verlauft (80-125 kJ mol-', je nach verwendetem Alkan), ist das homogene System Q,Wl,,032/Saure/Acetonitril/Alkan aufierordentlich wirksam fur die Umwandlung von Licht in chemische Energie. Absorptionsspektren, Redoxtitrationen und Quantenausbeuten als Funktion des Verhaltnisses [Saure]/ [Q4W10032] belegen, daR es sich bei der nach GI. (e) gebildeten reduzierten Spezies [W,oO,r]ne um das einfach protonierte, um zwei Elektronen reduzierte [H W,o032]5 handelt. Die Bildungsgeschwindigkeit von [HWlo032]5a ist erster Ordnung sowohl beziiglich der Lichtintensitat als auch bezuglich der Konzentration des Alkans und der Protonen bei niedrigen Konzentrationen; sie geht aber gegen nullte Ordnung fur hohere Konzentrationen beider Kornponenten. Bei ,,optisch dichten Bedingungen" ist die Geschwindigkeit praktisch unabhangig von der Konzentration des Katalysators [Wlo032]40, da alles eingestrahlte Licht vom Komplex absorbiert wird. Mit beiden Formen von [Wlo03r]4e -der protonierten und deprotoniertenkonnen Alkane photooxidiert werden.Eingegangen am 17. Mai, veranderte Fassung am 18. September 1988 [Z 27641 [I] Neuere Ubersicht: a) R. H. Crabtree, Chem. Reu. 85 (1985) 245: b) 1. P. Rothwell. Polyhedron 4 (1985) 177: c) M. Ephritikhine. NOUII. J. Chim. 10 (1986) 9. 121 Ubenicht fiber Metallporphyrin-katalysierte Oxidation: a) B. Meunier.Oxometall-Gruppen spielen bei einer Vielzahl metallvermittelter Urnwandlungen, von stochiometrischen Reaktionen uber die Heterogenkatalyse bis zu enzymatischen Prozessen, eine entscheidende Rolle'']. Die Reaktivitat der Metall-Sauerstoff-Mehrfachbindung reicht von sehr nied-
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