1.3- dihydro complex with

The reduction (136) of pyridinium compounds to 1,2- or 1,4-dihydro products with complex metal hydrides or dithionite leads to cyclic di-enamines of synthetic and biochemical interest. 

Dihydro-lH-l,2-azaboroles react with j7 -CpCo(C2H4)2 at —78°C giving mixed Tj -cyclopentadienyl-T7 -dihydroazaborole complexes with an 18-electron configuration ... 

One Rh complex with a 2,3-dihydro-l,3-diborolyl ligand is prepared by dehalo-genation of [(Et2C2B2Et2CMe)RhCl]2 with K in the presence of free 2,3-dihydro-1,3-diborole (Et2C2B2Et2CHMe)Rh(Et2C2B2Et2CMe) possesses one borole and one borolyl ring ligand. ... 

Some half-sandwich complexes with dihydro-l,2-azaborolyl ring ligands have been described, too ... 

A versatile route to 3-benzoheteropines has been reported starting from o-phthalaldehyde, including the first preparations of 3-benzarsepines and the parent 3-benzothiepin and 3-benzoselenepins <96CC2183>. l,7-Dihydro-l//-dibenzo[c,c]tellurepin has been prepared from 2,2 -bis(bromomethyl)biphenyl and potassium tellurocyanate and its complexes with palladium and ruthenium species have been studied, a number of mono- and binuclear complexes are formed <96RTC427>. 

Homoleptic gold(III) complexes with other related dithiolate ligands, as dmit (317),1855-1864 dddt,1865,1866 l,3,5-trithiepin-6,7-dithiolate,1867 dithiosquarate (318),1868,1869 6,7-dihydro-6-methy-lene-5H-l,4-dithiepine-2,3-dithiolate,1870 3,4-thiophenedithiolate (319),1637 quinoxaline-3,3-dithiolate (320),1871 2,2-diacetylethylene-1,1-dithiolate,1872 or o-carborane-1,2-dithiolate have been... 

Carbene complexes have also been prepared by transmetallation reactions. Lithiated azoles react with gold chloride compounds and after protonation or alkylation the corresponding dihydro-azol-ylidene compounds, e.g., (381) or (382), are obtained.22 9-2264 Silver salts of benz-imidazol have also been used to obtain carbene derivatives.2265 Mononuclear gold(I) carbene complexes also form when trimeric gold(I) imidazolyl reacts with ethyl chlorocarbonate or ethyl idodate.2266,2267 The treatment of gold halide complexes with 2-lithiated pyridine followed by protonation or alkylation also yields carbene complexes such as (383).2268 Some of these carbene complexes show luminescent properties.2269-2271... 

The reaction of [AuCl(THT)] with 2-(4,5,-dihydro-4,4,-dimethyl-2,-oxazolinyl)-thien- -yllthium (n = 3,5) affords dimeric (586) or trimeric (587) gold(I) derivatives with mixed /V,C-donor ligands.2263 Other complexes with mixed N,C donor ligands which have been prepared in a similar manner are [Au2 Fc(CFl2NMe2 2], 7 [Au2 C6Fl4(CFl2NMe2) 2],3132... 

The enhanced chemiluminescence associated with the autoxidation of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) in the presence of trace amounts of iron(II) is being used extensively for selective determination of Fe(II) under natural conditions (149-152). The specificity of the reaction is that iron(II) induces chemiluminescence with 02, but not with H202, which was utilized as an oxidizing agent in the determination of other trace metals. The oxidation of luminol by 02 is often referred to as an iron(II)-catalyzed process but it is not a catalytic reaction in reality because iron(II) is not involved in a redox cycle, rather it is oxidized to iron(III). In other words, the lower oxidation state metal ion should be regarded as a co-substrate in this system. Nevertheless, the reaction deserves attention because it is one of the few cases where a metal ion significantly affects the autoxidation kinetics of a substrate without actually forming a complex with it. 

The more hindered (37c) is to be preferred the PB is less susceptible to Michael addition and (37c) as well as (37cH) are less nucleophilic than those of the lower esters (see Sect. 14.8.5 for an example). In the absence of side reactions these PBs are, upon workup, converted into the dihydro derivatives that can be reoxidized back to the PBs by bromine or by anodic oxidation [68, 87, 88]. The base strength of (38) can be modified either by substitution [89] or by complexation with alkali metal counterions [86, 89]. 

Competitive lithiation cannot occur with monocyclic compounds, and clean a-lithiation was observed with the rhenium bis-(triphenylphosphine) dihydro complex at -78°C (Scheme 13) [89JOM(362)C31 90H(31)383]. So far, only reaction with alkyl halides has been reported, but presumably other electrophiles would react similarly. 

Reactions of cyclopentadienyl- and (pentmethylcyclopentadienyl)iron dicarbonyl 2-alkynyl complexes as well as cyclopentadienylmolybdenum tricarbonyl 2-alkynyl complexes with 4,5-diphenyl-3,6-dihydro-l,2-dithiin 1-oxide 111 were shown to yield transition metal-substituted five-membered ring thiosulfinate esters 112 in moderate to excellent yields (Scheme 27) <19910M2936, 1989JA8268>. These reactions are formal [3-1-2] cycloadditions. When... 

Evidence of the existence of oxidation state +IV is not yet convincing. Some complexes with dithiolene or dithiolate systems have been reported, such as [Au(5,6-dihydro-l,4-dithiin-2,3-dithiolate)2] (Figure 1.76) [350], or [Au(2,3-dithiophe-nedithiolate)2] [351]. They were prepared by chemical or electrochemical oxidation of... 

Many 1,2,4-triazines form complexes with metal ions and can be used for their determination. Thus, 3- and/or 5-(2-pyridyl)-substituted 1,2,4-triazines (e.g. 820) can be used for the determination of iron (II), cobalt(II), nickel(II), zinc(II) and copper(I) ions, thallium and palladium ions can be analyzed by 6-phenyl- (821a) and 5,6-diphenyl-l,2,4-triazine-3-thione (821b), while osmium can be determined by 3-thioxo-l,2,4-triazin-5-one (822), 3-thioxo-dihydro-l,2,4-triazin-5-one (823), 6-mercapto-l,2,4-triazine-3,5-dione (824a), 6-mercapto-5-thioxo-l,2,4-triazin-3-one (824b) and 3,5-dithioxo-l,2,4-triazine-6-carboxyl-ates (825) <78HC(33)189, p. 1004). 

The reaction of ethyl diazoacetate (312) with sodium or potassium ethoxide was studied by Curtius and his coworkers (08CB3140). They isolated a compound for which they proposed structure (316), which is a metal salt of diethyl l,6-dihydro-l,2,4,5-tetrazine-3,6-dicarboxy-late complexed with one mole of the ethoxide used. 

Asymmetric hydrosilylation.1 Hydrosilylation of the 3,4-dihydro-(2//)-pyr-roles (1) with (C6H5)2SiH2 catalyzed by [Rh(COD)Cl]2 complexed with ( + )- or ( - )DIOP can proceed with as much as 64% ee. (S)-Enantiomers are formed preferably with ( + )-DIOP (R)-enantiomers are favored with ( - )-DIOP. Example ... 

The reduction of ( )-2-, ( )-3- and ( )-4-cinnamoylpyridines by 1,4-dihydropyridines to give dihydro ketones has also been shown to be catalyzed by zinc(II) and magnesium(II).527 Kinetic measurements show that the rate of reduction is fastest in the case of the 2-isomer where the metal is simultaneously complexed with the nitrogen and oxygen donors. A very fast zinc-catalyzed reduction of pyridine-2-carbaldehyde by the alcohol dehydrogenase coenzyme model JV,JV -diethyl-N-benzyl-l,4-dihydronicotinamide (170) has also been described.528... 

HDS-relevant reactions with metal complexes, 1, 784 metal complex reactions, 1, 785 Dihydro(methyl) complexes, with platinum(IV), 8, 582... 

Pantolactone, dihydro-3-hydroxy-4//-dimethyl-2(3//)-furanone (103) which is an important starting material of the synthesis of pantothenic acid, was also easily resolved by complexation with 10a. When a solution of 10a (5.5 g, 9.93 mmol) and rac-103 (2.6 g, 20 mmol) in 1 1 benzene-hexane (20 ml) was kept at room temperature for 1 h, a 1 1 complex of 10a and (.S)-(-)- 03 was obtained, after two recrystallizations from 1 1 benzene-hexane, as colorless needles (2.05 g), which upon heating in vacuo gave (S)-(-)-103 of 99% ee (0.39 g, 30%).40 In order to clarify the mechanism of the precise chiral recognition between 10a and (S)-(-)-103, their inclusion complex crystal was studied by X-ray analysis40 and by AFM technique.41... 

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