Organometallic Compounds of Pyrrole

Nontransition metal cyclopentadienyl derivatives of pyrrole are quite scarce (99CRV969). The derivatives M(2,5-C4H2 Bu2N)2 (M = Sn, Pb) were studied [92AG(E)778 92JCS(CC)760]. 

Lithium tetramethylpyrrolate forms the if complexes 1 (n = 3,X = Cl) and 1 (n = 2,X = Cl) reacting with TaMe3Cl2 (96IC3228). Complex 1 (n = 3,X = Cl) enters a reaction with LiX (X = Me, pyrrolyl, indolyl) to yield 1 (n = 3, X = Me, A-pyrrolyl, A-indolyl), the latter two products being the mixed coordinated species. Both of them undergo thermolysis to give 1 (n = 2,X = A-pyrrolyl, 7V-indolyl). 

Reaction between [W(RC=C)Cl(CO)2(py)2] (R = Ph, Me) with the anionic chelating Schiff base pyrrole-2-carboxaldehyde methylimine yields the cationic complexes [NEt4][W(RCCO)(NN)2(CO)] (where NN is the dianion of the pyrrole ligand). These complexes react with methyltriflate, forming the neutral acetylenic complexes [W(NN)2(CO)(RC=COMe)] (87OM1503). One of the pyrrolic Schiff bases is coordinated via the pyrrole and imino nitrogen atoms, and another one only via the imino nitrogen atom. 

The nitrogen atom in iri -pyrrolylmanganesetricarbonyl forms a donor-acceptor bond with transition metals. Complexes in which the pyrrolyl ring behaves as a tt ligand for the manganese atom and /z-donor for the other metal were synthesized 12 (M = Mn, Re) [78JOM(157)431]. The binuclear heterobimetallic complexes 

r3 = r4 = H) [64J0M(1)471 68JOM(14)405 70JINC441 84JA1646 86JCS(F2)1543 90JOM(388)175]. During the formation of 20, it is possible to anticipate the existence of an intermediate a-pyrrolate complex 21, which then 

---

The fourth chapter of this volume comprises the second part of an ongoing series by Professor A. P. Sadimenko (Fort Hare University, South Africa) dealing with organometallic compounds of pyrrole, indole, carbazole, phospholes, siloles, and boroles. This follows the review in Volume 78 of Advances covering organometallic compounds of thiophene and furan. The enormous recent advances in this area are summarized and classified according to the nature of the heterocycle and of the metals. 

Analytical application of oligopyrrole macrocycles 01CCC693. Mechanisms of pyrrole electropolymerization 00CSR283. Organometallic compounds of pyrroles 01AHC(79)115. 

The a- (171-) complexes are known for pyrroles and phospholes. For pyrroles, both N-metal derivatives (10) and organometallic compounds (82) and (83) are described. A similar situation is observed in pyrrolylimido complexes Pwu-[MX(NNC4H4)(dppe)2]+ and cis,mer-[WX2(NNC4H4) (PMe2Ph)3], whose reaction ability has been studied comprehensively (95JA12181). A mixed 771 175 coordination is realized in the binuclear Cr(CO)5 complex of azaferrocene (90MI4). 

Heterocyclic aromatic compounds such as pyrrole are readily metallated with Grignard reagents. The resulting compounds have N"Mg bonds and are, therefore, not organometallic compounds, but on reaction with electrophiles give 2-substituted pyrroles [14] (eq (4)). The reaction of chloroform or bromoform with PrMgCl at -78 °C in THF-HMPA (4 1) is mild and convenient method for the generation of an unstable carbenoid in the solution [15] (eq (5)). 

Similar considerations have been made in the case of HDN-related substrates like pyrroles and pyridines. Nevertheless, the advances in this direction are much more modest and less clear-cut than those made for HDS models, and therefore, an exciting opportunity is open for new research in the organometallic modeling of the adsorption and reactivity of organonitrogen compounds. 

Two groups of elements appear in significant concentrations in the original crude oil, associated with well-defined types of compounds. Zinc, titanium, calcium, and magnesium appear in the form of organometallic soaps with surface-active properties, adsorbed in the water-oil interfaces, and act as emulsion stabilizers. However, vanadium, copper, nickel, and part of the iron found in crude oils seem to be in a different class and are present as oil-soluble compounds (Reynolds, 1997). These metals are capable of complexing with pyrrole pigment... 

A route to pyrroles illustrated by the preparation of 292 involves initial treatment of the nitroketene-5, 5 -acetal 293 with an organometallic reagent, followed by conversion of the resulting alkene 294 to the enamine 295, and final annulation to the target heterocycle (Scheme 34) <1998T12973>. A related approach featuring constmction of /3-hydroxyenamines from 1,3-dicarbonyl compounds and /3-amino alcohols, and subsequent palladium-catalyzed cyclization to pyrroles, has been reported <1996TL9203>. 

---