Iminoacyl complexes

Yamamoto and Yamazaki 171) carried out reactions of Pt(PEt3)2CHjI and Pt(PPhMe2)(CH2CjH5)I with tert-butyl and cyclohexyl isocyanides. These reactions gave small yields of the ionic intermediate species, which readily reverted to the appropriate iminoacyl complexes. In reactions of analogous chloride complexes the intermediate species was not isolated. It is suggested on the basis of PMR data that these iminoacyl complexes are five-coordinate (see above). 

Insertions of isocyanide into niobium-carbon bonds follow a path similar to that with vanadium, resulting in the formation of the 7]2-iminoacyl complexes, which can then be involved in further chemistry.175 176 The reaction of acetone with cyclopentadienyl complex 110 under a carbon monoxide atmosphere gives the if -acetone compound 111. Complex 111 subsequently undergoes either stepwise insertion of two isocyanides via 112 or double insertion of the isocyanide to give complex 113 (Scheme 48).177... 

A wide variety of five-membered zirconacydes 8 may be formed by the formal co-cycliza-tion of two 7i-components (3 and 6 alkene, alkyne, allene, imine, carbonyl, nitrile) on zir-conocene ( Cp2Zr ) (Scheme 3.2) [2,3,8]. The co-cydization takes place via the r 2-complex 5 of one of the components, which is usually formed by complexation of 3 with a zircono-cene equivalent (path a) ( Cp2Zr itself is probably too unstable to be a true intermediate) or by oxidation on the metal (cyclometallation/p-hydrogen elimination) (path b). Two additional routes to zirconocene r 2-complexes are by the reverse of the co-cyclization reaction (i. e. 8 reverting to 5 or 9 via 7), and by rearrangement of iminoacyl complexes (see Section... 

The synthesis of analogous iminoacyl complexes by isonitrile insertion into linear alkyl-zirconocene chlorides is also known. In an overall regiospecific hydrocyanation of alkenes, iminoacyls 21 derived from tBuNC or Me3SiCN (as the Me3SiNC isomer) may be treated with I2 to rapidly generate an imidoyl iodide and subsequently the nitrile 22 (Scheme 3.6) [22], Less hindered iminoacyl complexes (e. g. R = Bu, Cy) may be hydrolyzed to afford aldehydes 23 [23]. 

Isonitrile insertion into zirconacycles to afford iminoacyl complexes 28 is fast, but rearrangement to q2-imine complexes 30 is slow. In the case of tBuNC, the rearrangement does not occur. Amines 32 are formed on protonolysis of the q2-imine complex. The q2-imine complexes 30 readily undergo insertion of Ti-components (alkenes, alkynes, ketones, aldehydes, imines, isocyanates) to provide a wide variety of products 37 via zirconacycles 36. The overall sequence gives a nice demonstration of how a number of compo-... 

C-H bond dissociation energies, 1, 298 C-N triple bond additions, 10, 427 C02, ketene, ketenimine complexes, 5, 84 CO and CNR reductive coupling, 5, 66 cyclopentadienyl alkyl and aryls, 5, 66 cyclopentadienyl carbonyl complexes, 5, 64 cyclopentadienyl hydrides, 5, 69 cyclopentadienyl isocyanide complexes, 5, 65 rf-acyl and rj2-iminoacyl complexes, 5, 82 fj3-complexes, 5, 87... 

The use of the permethyltitanocene template 94 (Scheme 14) allows for the isolation of the intermediate iminoacyl complex 95, which was not observed in reactions using the substituted bis(indenyl)titanocene. 

Methylenezirconacyclobutane complex 99 undergoes double isonitrile insertion, but not reductive carbon-carbon bond formation, yielding the bis(iminoacyl) complex 100 (Scheme 16) <1994AGE2465>. Single insertion is observed using ftTf-butylisocyanate or methyl formate. 

The related ) -immoacyl complexes (124) are known ()] -C=N). These may be prepared by reaction of [Fe(CO)2(PMe3)2(Me)I] with t-butyl isocyanide, through an equilibrium with ] -iminoacyl complex (125). The equilibration is catalyzed by halide ion, NOs, and C104, but not by BF4, PFe , or BPlu consequently, the pure compounds are isolated by precipitating the BPli4 salt from the mixture. The mechanistic details of the equilibrium have been investigated in detail. ... 

Bonding of iron to the CO unit is not symmetrical Fe-C and Fe-O bond lengths of 1.8-1.83 and 2.19-2.25 A, respectively, are typical. IR spectra give a typical vc=o of 1586-1605 cm. The acyl carbon resonance appears at 280 ppm in the C NMR spectra but is not always observable at room temperature. Structurally, ) -iminoacyl complexes (124) are strictly analogous to ) -acyl complexes (115), with a C-N bond length intermediate between double and triple bond length (1.21-1.30 A). 

Treatment of Cp ( ) -C5Me4CH2)Ti with PbCb gives Cp (jj -C5Me4CH2)TiCl, which reacts with C=N(2,6-Me2C6H3) to give the ) -iminoacyl complex (36). Reaction of iminoacyl (28) with a second equivalent of isonitrile gives (37). ... 

Neutral and cationic homoleptic (see Homoleptic Compound) tnngsten-isocyanide complexes W(CNR)6 and [W(CNR)y] + (R = alkyl, aryl) are known, and W(CO)e (CNR) (n=l-3) complexes may be prepared from W(CO)6 and excess isocyanide in the presence of catalytic amounts of C0CI2 or PdO. Iso-cyanides are isoelecfronic with CO and also insert into the W-R bonds of alkyl complexes (see Alkyl Complexes). For instance, the alkyl-nitrosyl complexes Cp W(NO)(X)(CH2Bfr) (X = NHBfr, OBfr) react with CNBu to afford -iminoacyl complexes, and the isocyanide complexes, Cp W(CO)2(Me)(CNR) (10, R = alkyl), rearrange to afford either -iminoacyl Cp W(CO)2( -MeCNR)(ll) or ij -l-azaallyl Cp W(CO)2( -CH2CHNR) (12) derivatives, depending upon the reaction conditions (equation 4). ... 

Insertion of isonitriles into zirconacycles affords )] -iminoacyl complexes that smoothly rearrange to stable f-irame zirconocenes. In the case of 2-phosphanozirconaindenes, rearrangement proceeds leading to -imine zirconocenes (Scheme 35). Subsequent formation of a /3-phosphano indenoimine is obtained by elimination of Cp2Zr fragment for the 2,6-dimethylphenyl isocyanide." ... 

Isonitrile is isoelectronic with CO, and iminoacyl complexes can be compared with acyl ones. The most remarkable difference is that isonitrile undergoes multiple insertion, not observed in CO, into transition-mctal-carbon bonds to produce bis-, tris- or poly(imino) complexes . ... 

The Pt analog does not react, but an iminoacyl complex is ultimately prepared on heating at 80°C . The iron complex, -CpFe(COXCNC6H,X4-RC6H4CH2), under-... 

A dimeric iminoacyl complex forms an addition of cis-/f-bromoacrylate to [Pd(CNBu-t)2] (the halogen bridges are cleavage bases such as isonitrile and phosphine ) ... 

The anion [>j -CpMo(CO)2(CNR)] (R = Me or Ph) reacts with Mel in THF at — 78°C to form the neutral iminoacyl complex, which contains a novel r/ -iminoacyl ligand. This complex adds donor ligands L, such as PPh3 and P(OMe)3, to produce the corresponding >/ -iminoacyl complex ... 

The iminoacyl complexes of Ti Zr pjf Ta and U are also obtained. Examples are given in Table 1. 

The Tj -iminoacyl complexes 354 react with CO to give the corresponding amidoenolato complexes 355 . Similarly, the reaction between 356 and CO gives 357 °. 

Interestingly, Bochmann el at. have characterized several Ti(IV) RNC adducts which are rare examples of cP metal isocyanide complexes (39). The reaction of (C5H5)2Ti(CH3)(CH3CN)+ with RNC (R = Bu, SiMe3) yields the iminoacyl complexes (C5H5)2Ti(/ -C(Me)=NR (CNR)+ via insertion of and trapping by RNC. The BuNC complex Cp 2Ti(CH3)(CN Bu)+ is observed as an intermediate in the analogous... 

Insertion of isocyanide groups into metal-carbon bonds yields > -iminoacyl complexes reaction (n), which are briefly considered as belonging to both 1,1- and 1,2-insertions reactions on the basis of the binding. 

The 1,2-insertion of isocyanides into a metal-carbon bond occurs readily to yield t -iminoacyl complexes... 

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