Trimethylenemethane ligand

The symmetrical structure of the trimethylenemethane ligand is indicated in solution by the n.m.r. spectrum which shows three resonances 211.6... 

Another general way to prepare trimethylenemethane complexes is the reaction of trimethylenmethane dianions with metal halides. By this way. Mills et al. obtained (cyclopentadienyl)(trimethylenemethane)cobalt (21) in 18% yield by dilithiation of isobutene (19) with butyllithium/tetramethylethylenediamine (TMEDA) to dianion 20 [22,23] followed by treatment with 1 equiv. of (cyclopen-tadienyl)diiodo(triphenylphosphane)cobalt (Scheme 10.7). The crystal structure analysis shows a highly symmetric molecule with a slight pyramidalization of the trimethylenemethane ligand away from the cyclopentadienylcobalt... 

Bergman et al. presented a reaction sequence, in which a neopentyl ligand at a tripod ruthenium(II) complex degraded stepwise to a trimethylenemethane ligand. The reaction sequence from 29 via 30 to 31 involves C,C- and C,H-activation steps (Scheme 10.11) [29]. 

A new mode of bonding for the trimethylenemethane ligand is found in [ZrCp 2 r 3-(CH2)2CCH2 ], prepared by reaction of [Cp 2ZrCl2] with Li2[TMM(tmeda)]. X-ray crystallography showed the ligand to be T)3-coordinated with two strong Zr-CH2 o-bonds and a weak interaction to the central carbon. ... 

In trimethylenemethane complexes, the metal stabilizes an unusual and highly reactive ligand which cannot be obtained in free form. Trimethylenemethanetricar-bonyliron (R=H) was the first complex of this kind described in 1966 by Emerson and coworkers (Figure 1.2) [38]. It can be obtained by reaction of bromomethallyl alcohol with Fe(CO)5. Trimethylenemethaneiron complexes have been applied for [3+2]-cycloaddition reactions with alkenes [39]. 

TCNE = Tetracyanoethylene Dipdba = 4,4 -diisopropyl(di-benzylideneacetone) TMM = Trimethylenemethane dppm = (Diphenylphosphino)methane MMLCT = Metal-metal bond to ligand charge-transfer Tp = Hydrido(trispy-razolyl)borate Tp = Hydridotris(3,5-dimethyl-pyrazolyl)bo-rate BAr = (3,5-triflnoromethylphenyl)borate ttab = l,2,4,5-tetrakis(l-iV-7-azaindolyl)benzene tmeda = Tetra-methylethylenediamine bpma = Bis(pyridyhnethyl)amine TFE = Triflnoroethanol dtbpm = Bis(di-terr-butylphosphi-no)methane dmpe = Bis(dimethylphosphino)ethane dcpe = Bis(dicyclohexylphosphino)ethane triphos = Bis(2-diphe-nylphosphinoethyl)phenylphosphine COD = 1,5-cycloocta-diene dppbts = (Diphenylphosphinobutane)tosylate sodium PPE = Poly(jo-phenylene ethylene). 

Thus, the amount of phosphane added can be used to markedly influence the product distribution when 2-substituted methylenecyclopropanes are used as substrates. A possible explanation of this observation might lie in the ability of a strong donor ligand, such as an alkylphosphane, to prevent a hapticity change of the ring-cleaved methylenecyclopropane from 1/ -coordination (allyl-type) to 1/ -coordination (trimethylenemethane-type), which is indispensable for induction of the scrambling reaction. 

Figure 4.9. Frontier orbitals available for metal-carbon bonding in complexes of acyclic unsaturated systems C I I 2- (a) Allyl ligand H2CCHCH2 (b) buta-l,3-diene H2C=CHCH=CH2 (c) trimethylenemethane 6(012)3.

Cycloaddition reactions. The aminophosphite Hg-2C derived from octahydro-BINOL is found to promote the [3+3]cycloaddition of nitrones and trimethylenemethane derivatives to furnish 1,2-oxazines. Remarkable ligand effects have been observed in the spiroannulation of oxindoles products possessing opposite configuration at the spirocyclic center arise by changing the naphthyl substituents on the pyrrolidine ring (7A [a-Np] vs. 7B [P-Np])."... 

The bis-(P-naphthyl)pyrrolidinyl-containing ligand also finds use to induce chirality in the trimethylenemethane cycloaddition to imines, which leads to 2-substituted... 

TCNE = Tetracyanoethylene Dipdba = 4,4 -diisopropyl(di-benzylideneacetone) TMM = Trimethylenemethane dppm = (Diphenylphosphino) methane MMLCT = Metal-metal bond to ligand charge-transfer Tp = Hydrido(trispy-razolyl)borate Tp = Hydridotris(3,5-dimethyl-pyrazolyl)bo-rate BAr 4 = (3,5-trifluoromethylphenyl) borate ttab =... 

The Trost group has devised a strategy for stereoselective spirocyclic ring installation across 3-alkylidene oxindoles via palladium-catalyzed [3-1-2] cycloaddition with cyano-substituted trimethylenemethane (Scheme 33) [74, 75]. As illustrated, the opposite sense of diastereoselectivity was observed depending on the choice of chiral ligand 125 or 126. Preferential orientation of the benzenoid portion of the oxindole as dictated by the varied steric environments of the naphthyl ring systems on the catalysts has been put forth as a rationale for the observed difference in stereochemical outcomes. Spirooxindoles 127 and 128 were obtained in 92% ee and 99% ee, respectively. A variation of this methodology has been applied in the racemic synthesis of marcfortine B [75]. 

In this latter reaction mode, which is observed much more rarely than /3-dehydropal-ladation, a wide variety of ligands can be coupled to each other with the formation of new C—C, C—H, C— N, C—O, and C—Hal bonds. This section does not cover the numerous cascade couplings in which a number of successive intramolecular additions of 2 onto double bonds is eventually completed by /3-dehydropalladationt as well as the numerous [2 -I- 2 -I- 2] and [4 + 2] cyclotri- and cyclodimerizations of alkynes, enynes, and related compounds. " The Pd(0)-catalyzed Cope rearrangement also will not be considered here, as it proceeds via bis(i7 -allyl)palladium(ll) intermediates. The carbopalladation reactions of aUenes, which have been reviewed recently, are covered in Sect. IV.7. (For new examples see also refs. [10]-[12]). On the other hand, the numerous Pd-catalyzed formal [3 + 2] cycloadditions of trimethylenemethane (TMM) complexes may be classified as carbopalladations of alkenes without subsequent dehydropalladation. As the subject of this section has partially been covered in several newly published reviews, " the attention here will be on the most recent and interesting communications. 

The AlCl3-catalysed 3-I-2-cycloaddition of diethyl frans -2,3-disubstituted cyclopropane-1,1-dicarboxylates and aromatic aldehydes produced diethyl 2,5-diaryl-4-benzoyltetrahydrofuran-3,3-dicarboxylates in moderate to good yields and with excellent diastereo-selectivities. The palladium-catalysed 3 -f- 2-cycloaddition of trimethylenemethane with aldehydes produced methylenetetrahydrofurans in good yields and with good enantioselectivities. A novel phosphoramidite ligand possessing a stereogenic phosphorous (29) was used in this transformation. ... 

Nucleophilic attack on coordinated unsaturated hydrocarbons is one of the fundamental and particularly well studied reactions in Organometallic Chemistry. The addition of carbonylme-tallates instead of common nucleophiles provides a directed synthesis of hydrocarbon bridged complexes. Carbonylmetallates (particularly Re(CO)5", Os(CO)4 ") add to 7C-bonded olefin, acetylene, allyl, diene, trimethylenemethane, dienyl, benzene, triene and cycloheptatrienyl ligands in cationic complexes and give hydrocarbon bridged bi- and trimetallic, homo- or he-teronuclear complexes [1]. 

The following compounds are classified as Ae ligands 1,3-dienes, cyclobutadiene, and trimethylenemethane, and their derivatives. 

Figure 8.1. Molecular orbitals of (a) 1,3-dienes, (b) cyclobutadiene, (c) trimethylenemethane. Metal orbitals which may form bonds with the given orbital of the ligand are shown.

In trimethylenemethane complexes, the metal atom is located under the central carbon atom. The terminal carbon atoms of the ligand are located in a plane which is closer to the metal atom than the central carbon, and therefore all metal-carbon distances are the same. Thus, the coordinated trimethylenemethane molecule is bent and possesses symmetry. The structures of complexes containing 4c ligands are represented in Figures 8.5 and 8.6, and the interatomic distances are given in Table 8.2. 

For cyclobutadiene complexes, the energy of activation of rotation of ligands about the M-C4R4 axis is very small, while for the trimethylenemethane iron derivative the AG of rotation of trimethylenemethane is high, equaling 71-75 kJ mol (Table 8.4). 

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