Platinum complexes allenes

A derivative of cyclopentyne has been trapped in a matrix. Although cycloheptyne and cyclohexyne have not been isolated at room temperatures, Pt(0) complexes of these compounds have been prepared and are stable." The smallest cyclic allene" so far isolated is l-/err-butyl-l,2-cyclooctadiene 107." The parent 1,2-cyclooctadiene has not been isolated. It has been shown to exist transiently, but rapidly dimerizes." " The presence of the rert-butyl group apparently prevents this. The transient existence of 1,2-cycloheptadiene has also been shown," and both 1,2-cyclooctadiene and 1,2-cycloheptadiene have been isolated in platinum complexes." 1,2-Cyclohexadiene has been trapped at low temperatures, and its structure has been proved by spectral smdies." Cyclic allenes in general are less strained than their acetylenic isomers." The cyclic cumulene 1,2,3-cyclononatriene has also been synthesized and is reasonably stable in solution at room temperature in the absence of air." ... 

Introduction of the allene structure into cycloalkanes such as in 1,2-cyclononadiene (727) provides another approach to chiral cycloalkenes of sufficient enantiomeric stability. Although 127 has to be classified as an axial chiral compound like other C2-allenes it is included in this survey because of its obvious relation to ( )-cyclooctene as also can be seen from chemical correlations vide infra). Racemic 127 was resolved either through diastereomeric platinum complexes 143) or by ring enlargement via the dibromocarbene adduct 128 of optically active (J3)-cyclooctene (see 4.2) with methyllithium 143) — a method already used for the preparation of racemic 127. The first method afforded a product of 44 % enantiomeric purity whereas 127 obtained from ( )-cyclooctene had a rotation [a]D of 170-175°. The chirality of 127 was established by correlation with (+)(S)-( )-cyclooctene which in a stereoselective reaction with dibromocarbene afforded (—)-dibromo-trans-bicyclo[6.1 0]nonane 128) 144). Its absolute stereochemistry was determined by the Thyvoet-method as (1R, 87 ) and served as a key intermediate for the correlation with 727 ring expansion induced... 

Resolution of lj-cyclononadiene. Cope et al. examined the resolution of the cyclic allene 1,2-cyclononadiene (1) by way of the diastereomeric platinum complex containing this amine (compare resolution of cycloalkenes (2, 272-273)). A... 

Another route to p.-Carbido complexes which we have found is oxidative addition of Lalor s halocarbyne complexes [21] to zero valent triphenylphosphine compounds of nickel, palladium and platinum. In these reactions the heterodimetalla cyclopropenes could be isolated which isomerize at higher temperatures to the dimetalla allene complexes. The first adducts of arylcarbyne complexes to zerovalent platinum complexes (arylcarbyne as analogue of ace-... 

A series of chloro(methyl)platinum complexes having 2,9-dimethyl-l,10- phenanthroline are obtained as the adducts of alkenes, allene, and GO (23-27, Scheme Not only does coordination of the unsaturated molecule... 

Gomprehensive reviews of the chemistry of heavy allenes and cumulenes, heteroaldehyde, heteroketone, phosphaalkene " " and 77 -ketenyl (77 -G(PPh3)=GO) " complexes, which include platinum complexes, have been published. A review of transition metal complexes of arynes, strained cyclic alkynes, and strained cyclic cumulenes also includes information relative to this section. " ... 

Platinum complexes also exhibit catalytic activity toward the carbonylation of allene with CO and aliphatic thiol can react with allene regioselectively [12]. The PtCl2(PPh3)2-catalyzed carbonylative thiolation of cyclohexylallene with I " Hex-SH) as an aliphatic thiol carbon monoxide by the use of aliphatic thiol ( Hex-CH) proceeds regioselectively at the terminal double bond of the allene. In the case of Pt(PPh3)4-catalyzed reaction, the thiolative carbonylation takes place at both terminal and central double bonds (Scheme 11.9). 

A series of covalent 96 and ionic 97 platinum complexes with chiral amine hgands (Figure 50.27) are effective chiral discriminating agents for alkenes and allenes. The substrate displaces the ethylene, and the Pt NMR spectrum is used for the determination of enantiomeric purity. Whether to use the ionic or covalent complex, and which amine hgand to use, depends on the substrate. Recommendations for the optimal reagent for different classes of substrates have been summarized in prior reports. ... 

When the transition-metal-catalyzed hydrothiolation of unsaturated compounds is performed in the presence of carbon monoxide, carbonylation reactions may proceed with the introduction of sulfanyl groups. In fact, a series of carbonylative thiolation reactions of alkynes and allenes are reported. These reactions provide useful tools to synthetically important organosulfur compounds [104, 105]. For example, the rhodium-catalyzed reaction of alkynes with thiols and CO provides the corresponding thioformylation products regioselectively [106, 107]. Switching the catalyst from rhodium complex to platinum complex leads to a sharp reversal of regioselectivity of CO introduction [108, 109] (Scheme 32). 

Complexes involving oxime ligands display a variety of reactivity modes that lead to unusual types of chemical compounds. As far as the oxime chemistry of platinum is concerned, these complexes are involved in facile deprotonation of the OH group with formation of oximato complexes, reduction of Pt(IV) species, Pt(II)-assisted reactions with coordinated allene," alkylation by ketones, oxime-ligand-supported stabilization of Pt(III)—Pt(III) compounds, oxidative conversion into rare nitrosoalkane platinum(II) species, and coupling with organocyanamides. ... 

Bis(phosphoranimine) ligands, chromium complexes, 5, 359 Bis(pinacolato)diboranes activated alkene additions, 10, 731—732 for alkyl group functionalization, 10, 110 alkyne additions, 10, 728 allene additions, 10, 730 carbenoid additions, 10, 733 diazoalkane additions, 10, 733 imine additions, 10, 733 methylenecyclopropane additions, 10, 733 Bisporphyrins, in organometallic synthesis, 1, 71 Bis(pyrazol-l-yl)borane acetyl complexes, with iron, 6, 88 Bis(pyrazolyl)borates, in platinum(II) complexes, 8, 503 Bispyrazolyl-methane rhodium complex, preparation, 7, 185 Bis(pyrazolyl)methanes, in platinum(II) complexes, 8, 503 Bis(3-pyrazolyl)nickel complexes, preparation, 8, 80-81 Bis(2-pyridyl)amines... 

Salvadori, R, Uccello-Barretta, G. and Lazzaroni, R. (1990) A new method for the enantiomeric excess determination of chiral trisubstituted allenes by 195Pt NMR of traKi-dichloro[(S)-a-methylbenzylamine](allene)platinum(II) complexes. /. Chem. Soc. Chem. Commun., 1121-1123. 

The bis(triphenylphosphine)platinum(0) complex of cyclopentyne (240) [Eq. (32)] is the only complex of a five-membered cycloalkyne that is discussed in an earlier review.2 The mechanism of its preparation is significant because 239 was isolated and shown to react with Na/Hg to give 240, thus suggesting that 7r-complexes may play a role in the formation of dw complexes of larger cycloalkynes2 36 82 and, possibly, cyclic allenes (Section IV)82 where trapping of the free intermediate had often been presumed. 

Unsuccessful attempts to prepare stable complexes of six-membered ring allenes that succeeded for their seven-membered counterparts (Section IV,C) include reaction of 299 with KOt-Bu in the presence of tris(triphenyl-phosphine)platinum(O) [Eq. (50)]118 and abstraction of methoxy from 301 (Scheme 37)119120 (L = CO) with trimethylsilyl triflate. The latter gave products suggestive of an intermediate complex of 1,2-cyclohexadiene, but it could not be detected or trapped. Based on fluxionality studies in the seven-membered counterpart (Section IV,C), equilibration of 302 with a... 

Reactions of complexes of 1,2-cycloheptadienes have received only cursory attention. 1,2-cycloheptadiene is readily displaced from bisftriphenyl-phosphine)platinum(O)118 [Eq. (54)], but no reagent has been found that will displace the allene from iron.119 Reaction of the iron complex with alcohol in the presence of base (e.g., 312 — 322) is typical of Fp+ complexes of acyclic allenes.131132 The thermal chemistry of 312 is unusual in its decomposition to 324 (Scheme 41). This is probably attributable to the presence of the triflate counterion, since the corresponding fluoroborate salt is stable when warmed to 40°C for 16 h.119 A mechanism to 324 via carbene complex 321 appears likely. 

Pt(0) complexes 343, 344, and 345, all of which have allene ground states, were prepared as illustrated and in Scheme 43 for 343 by treating appropriate bromocycloheptatrienes with KOr-Bu in the presence of tris (triphenylphosphine)platinum(O). The mechanism of this reaction is in ques-... 

Recent structural and spectroscopic investigations of organometallic complexes bonding two carbons of an allenic ligand to one rhodium 50 72> 87,95) or platinum atom 58,87,98,132) may have some pertinence to possible bridged intermediates proposed for various electrophilic additions to allenes, and the cr-iron-jr-iron complexes derived from allene and diiron... 

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