Complexes hexacarbonyl derivatives

Wong, Y.S., Paik, Fl.N., Chieh, P.C., and Carty, A.J., Two-carbon three-electron ligands. Phosphonium-betaine complexes via nucleophilic attack by phosphites on a o-rc-acetylide di-iron hexacarbonyl derivative, /. Chem. Soc., Chem. Commun., 309, 1975. 

The crystal structure of 2-lithiated l-methyl-l,3-benzazaphosphole 35 showed it to have a dimeric structure with two THF molecules associated with each lithium. The two lithium atoms and the two C-2 atoms form a four-membered ring <20020M912>. In contrast, the N-lithiated derivative of 2,5-dimethyl-l//-l,3-benzazaphosphole exists as a monomeric species 36 in the solid state <2002JOM(646)113>. The carbene-type complex 37 derived from the lithiated species 35 on reaction with tungsten hexacarbonyl was also studied by X-ray crystallography. 

The reactions of the phosphabenzene system [124] confirm these conclusions. Phosphabenzenes have low basicity towards hard acids. They are not protonated by CF3CO2H nor alkylated by trialkyloxonium salts. However, soft acids attack at phosphorus. For instance, 2,4,6-triphenyl-phosphabenzene forms compounds 4 with the hexacarbonyl derivatives of Cr, W and Mo in which the phosphorus coordinates to the metal, possibly with metal-P back-donation. The complexes 4 rearrange photochemically or thermally affording the 67i-heteroarene complexes 5. Although 2,4,6-triphenyl-pyridine is protonated on nitrogen, it undergoes complex formation with chromium hexacarbonyl exclusively on the phenyl moieties yielding the ri -arene complexes 6 [125]. 

We envisioned that an alkynyl substituent on a cyclopropane could be complexed as a cobalt hexacarbonyl derivative [8], which would enable activation of the cyclopropane toward ring opening in order to undergo subsequent cycloadditions. This is explained by the ring-opening of a cobalt complexed cyclopropanediester I under the influence of a Lewis acid to form the Nicholas carbocation 2 as illustrated in Scheme 10.3. 

The TT-complex 63 was obtained by the condensation of chromium hexacarbonyl with the thiophene a-derivative of dicarbonylironcyclopentadienyl 64 (76IZV153, 79IZV900). The presence of the electron-donor iron-containing substituent facilitates TT-coordination. 

Molybdenum and tungsten hexacarbonyls are able to form anionic complexes (AsPli4)2[(OC)4M( -pz)2M(CO)4] upon reaction with sodium pyrazolate and PluAsCl (72CB3203). The cationic complexes [(rj -Cp)2Mo(/Lt-pz)2Mo(rj -Cp)2] " (n = 2, 3) are known as well (74HCA1988). The other representatives of the complexes containing an exobidentate ligand (26) are derived from 4//-pyrazoles [70ZAAC(379)169]. 

Two S/P ligands derived from camphor, CamPHOS and MeCamPHOS were also developed by these authors for the diastereoselective coordination to alkyne-hexacarbonyldicobalt complexes (Scheme 10.68). These two ligands were converted in good yields into their borane-protected forms. The influence of the alkyne group (R) on their coordination to dicobalt-hexacarbonyl-alkyne complexes was evaluated. It was shown that MeCamPHOS ligand provided a... 

Optically active (—)-(8R)-methylcanadine was stereoselectively synthesized through selective monocomplexation of (—)-canadine (26) to chromium tricarbonyl (240). Heating of chromium hexacarbonyl with 26 effected regioselective complexation of the D ring to give the diastereomeric complexes, which were treated with n-butyllithium and trimethylsilyl chloride to give the 11-trimethylsilyl derivative 475 (Scheme 97). Methylation of this complex with methyl iodide gave stereoselectively the 8-methyl derivative 476 by preferential alkylation from the opposite face to the bulky chromium... 

The formation of 2H-pyrroles (21) and a pyrrole derivative (22) from the reaction of 3-phenyl-2//-azirines and acetylenic esters in the presence of molybdenum hexacarbonyl is intriguing mechanistically (Schemes 24, 25).53 Carbon-nitrogen bond cleavage must occur perhaps via a molybdenum complex (cf. 23 in Scheme 26) but intermediate organometallic species have not yet been isolated.53 Despite the relatively poor yields of 2H-pyrrole products, the process is synthetically valuable since the equivalent uncatalyzed photochemical process produces isomeric 2H-pyrroles from a primary reaction of azirine C—C cleavage54 (Scheme 24). 

Bromobenzyl alcohol and its derivatives were converted to phthalides by the palladium catalysed insertion of carbon monoxide and intramolecular quenching of the formed acylpalladium complex. 2-Hydroxymethyl-1-bromonaphthaline, for example, gave the tricyclic product in excellent yield (3.34.). An interesting feature of the process is the use of molybdenum hexacarbonyl as carbon monoxide source. The reaction was also extended to isoindolones, phthalimides and dihydro-benzopyranones 42... 

The extensive organometallic chemistry of chromium, i.e. the hexacarbonyl and its derivatives, organochromium compounds without carbonyl ligands, cyanide and isocyanide complexes, alkene, allyl, diene, cyclopentadiene and arene derivatives, and complexes of a-donor carbon ligands, has been recorded in Chapters 26.1 and 26.2 of Volume 3 of Comprehensive Organometallic Chemistry .1 In the present section, chromium complexes... 

More recently Voelter reported a related approach using a carbon tether to carry the yne derivatives [132], The formation of these branched-chain sugars has been described in Section II.B. Formation of the hexacarbonyl dicobalt complex from ene-yne 169 in benzene, followed by heating in DMSO yields the biscyclopentano sugar derivative 170. 

W. E. Undsell, P. N. Preston, and A. B. Rettie, Synthesis and characterisation of hexacarbonyl-dicobalt complexes derived from 2-propynyl and 3-butynyl 4,6-di-0-acctyl-2,3-dideoxy-a-D-ery(hro-hex-2-enopyranosides, Carbohydr. Res. 254 311 (1994). 

The IR spectra indicated the presence of disubstituted hexacarbonyl-metal derivatives with two different ligands in trans positions (trans-(CO MR R2). Moreover, the cryoscopic molecular weight determination proved that the complexes must be monomers. 

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