Metal propargyl complexes

Dipolar cycloaddition reactions are most commonly applied for the synthesis of five-membered heterocyclic compounds.86 87 [3+2] cycloaddition reactions of transition-metal propargyl complexes have been reviewed.88 Addition of diazomethane to carbene complexes (CO)5Cr= C(OEt)R results in cleavage of the M = C bond with formation of enol ethers H2C = C(OEt)R,3 89 but (l-alkynyl)carbene complexes undergo 1,3-dipolar cycloaddition reactions at the M = C as well as at the C=C bond. Compound lb (M = W, R = Ph) affords a mixture of pyrazole derivatives 61 and 62 with 1 eq diazomethane,90 but compound 62 is obtained as sole... 

Virtually all of the transition metal-propargyl complexes investigated react readily with either neat SO2 or SO2 in organic solvents according to Eq. (24), where M = CpFe(CO)2 (111, 124), CpMo(CO)3 (111, 124),... 

The most direct and successful synthesis of metal propargyl complexes involves nucleophilic attack of a metal carbonylate anion at a propargyl halide (9a-c,IO) [Eqs. (1) and (2)]. The propargylic products isolated... 

Only recently have early transition metal propargylic complexes been recognized. The lanthanide alkyls [LnCH(SiMe4)2(i7 -C5Me5)2j (Ln = La. Ce) react with the 2-alkynes MeC=CR (R = Me, Et, "Pr) to afford 1,2-disubstituted 3-alkylidenecyclobutenes. The first step in this catalytic cy-... 

Early investigations into the chemistry of tr-bound transition metal propargyl complexes concentrated on their reactivity toward charged and uncharged electrophiles. In the former case r/ -bound allene complexes [ML (r --CH2=C=CH2)]" were formed via protonation [Eq. (21)]... 

C2.12 Transition metal propargyl complexes versatile reagents in synthesis... 

The isomerisation of allyl and propargylic alcohols involves the 1,3-shift of an oxygen atom rather than a hydrogen atom. Isomerisation of allyl alcohols can be catalysed by a variety of metal oxo complexes and in this instance the reaction does not involve metal carbon bonds as we will see. One could imagine that allylic metal species can participate in isomerisation of allylic compounds, but for the alcohols themselves this is not an easy reaction. In chapter 13 reactions of allyl acetates and the like, which are more prone to... 

The reactions are those of functionalized 1-alkynes, the first of which were described for alkynes bearing substituted hydroxymethyl groups, such as substituted propargyl alcohols, HC=CCRR (OH), and often proceed further to form metal allenylidene complexes, by spontaneous dehydration of a (usually unobserved) hydroxy-vinylidene complex (Equation 1.22) ... 

In parallel, since the first preparation of allenylidene-metal complexes in 1976, the formation of these carbon-rich complexes developed rapidly after the discovery, in 1982, that allenylidene-metal intermediates could be easily formed directly from terminal propargylic alcohols via vinylidene-metal intermediates. This decisive step has led to regioselective catalytic transformations of propargylic derivatives via carbon(l)-atom bond formation or alternately to propargylation. Due to their rearrangement into indenylidene complexes, metal-allenylidene complexes were also found to be catalyst precursors for olefin and enyne metathesis. 

Since the first discovery of transition metal allenylidene complexes (M=G=C=C<) in 1976, " these complexes have attracted a great deal of attention as a new type of organometallic intermediates. Among a variety of such complexes, cationic ruthenium allenylidene complexes Ru =C=C=GR R, readily available by dehydration of propargylic alcohols coordinated to an unsaturated metal center, can be regarded as stabilized propargylic cation equivalents because of the extensive contribution of the ruthenium-alkynyl resonance form... 

In fact, this approach constituted one of the earliest trials. One is introduction of a chiral ligand like glyphos on cobalt by replacing one of the carbon monoxides to obtain an enantiomerically enriched new metal-alkyne complex. The second approach is use of the propargyl alcohol bearing a chiral auxiliary. Replacement of only one carbon monoxide would lead to a mixture of diastereomers. In both cases, a I I mixture of products was obtained, and each diastereomer was separated before the... 

Once an alkyne moiety is introduced into a peptide, e.g., as propargyl glycine (Pgl) in place of a simple glycine in Enk, it can of course be used directly for complexation to a metal complex. Along those lines, we have reacted Co2(CO)g with the peptide Ac-Tyr-Gly-Pgl-Phe-Leu-NH2, to yield the Co2(CO)6 complexed to the Pgl alkyne side chain [32]. In a real SPPS scheme with a pre-formed metal-alkyne complex, the amino acid building block [Tp WI(CO)(ri2-Fmoc-Pgl-OH)] was incorporated to yield the side-chain substituted Enk derivative H-Tyr-Gly-[Tp W(I)(CO)(r 2-Pgl)]-Phe-Leu-OH (Tp tris(3,5-dimethylpyrazolyl)-borate) [44]. 

Varghese V, Saha M, Nicholas KM (1988) Org Synth 67 141 Nicholas KM (1987) Acc Chem Res 20 207 Caffyn AJM, Nicholas KM (1995) Transition metal alkyne complexes transition metal stabilized propargyl system. In Abel EW, Stone FGA, Wilkinson G (eds) Comprehensive organometallic chemistry II, vol 12. Pergamon Press, Oxford, p 685 Schreiber SL, Klimas MT, Sammakia T (1987) J Am Chem Soc 109 5749 Nakamura T, Matsui T, Ta-nino K, Kuwajima I (1997) J Org Chem 62 3032... 

Metal-allyl complexes of formulas CpFe(CO)aCHaC(R) = CR R" and CpMo(CO)3CHaC(R) = CR R", as well as analogous propargyl and cyclopropylmethyl complexes, react with (CN)aC=C(CN)a to give cycloaddition products 21a, 56, 120, 121) of the type discussed in Section V. 

Metal Fragment Condensation Reactions with Propargylic Complexes... 

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