Monomeric complexes

There is much discussion on the nature of the aluminum species present in slightly acidic and basic solutions. There is general agreement that in solutions below pH 4, the mononuclear Al " exists coordinated by six water molecules, ie, [ ( 20) ". The strong positive charge of the Al " ion polarizes each water molecule and as the pH is increased, a proton is eventually released, forming the monomeric complex ion [A1(0H)(H20) ]. At about pH 5, this complex ion and the hexahydrated Al " are in equal abundance. The pentahydrate complex ion may dimerize by losing two water molecules... 

The aqueous U(VI) carbonate system has been very thoroughly studied, and there is Htde doubt about the compositions of the three monomeric complexes U02(C02), U02(C02) 2 U02(C02) 3 present under the appropriate conditions (154). There is also a great deal of evidence from emf,... 

The tetraimidosulfate anion [S(NtBu)4] , isoelectronic with 804 , is prepared by a methodology similar to that employed for the synthesis of triimidosulfites. The reaction of the sulfur triimide S(N Bu)3 with two equivalents of LiNH Bu produces the solvated monomeric complex [(thf)4Li2S(N Bu)4] (10.21) (Eq. 10.8). The nucleophilic addition of... 

Much effort has been invested into the search for monomeric compounds [86-90]. One of the few reliable indications for a base-stabilized monomeric complex involved the use of spectroscopic methods. The complexes 1 and 2 could be isolated and characterized below —20 °C with spectroscopic methods [91],... 

The coordination of [Me2Sn(IV)f to captopril (cap) [(2S)-l-[(2S)-2-methyl-3-sulfanyl propanoyl]pyrrolidine-2-carboxylic acid] in aqueous solution was studied by means of pH-metric titration, electrospray mass spectrometry, H NMR, and Mossbauer spectroscopies in the 2-11 pH range. The results obtained proved that only monomeric complexes are formed in solution. In the acidic pH... 

Fig. 14. Dimeric 38 is a cis-lactim derivative, while tetrameric 40 and oligomeric 35 are trans-lactim derivatives with a partially delocalized N—C—O central moiety. 36 and 39 are monomeric complexes...

The formation of dimeric products is unique for the case of boron, because analogous complexes with other elements are all monomeric [95]. This can be attributed to the small covalent radius of the boron atom and its tetrahedral geometry in four-coordinate boron complexes. Molecular modeling shows that bipyramidal-trigonal and octahedral coordination geometries are more favorable for the formation of monomeric complexes with these ligands. 

Rh(III)(NHC) hydrides have been studied as catalysts for this type of hydrogenation. The products from the reaction of Rh(I) complexes with are dependent on the natnre of the NHC. The reaction of [RhCl(IPr)2(N2)] 1 (IPr = Af,A -bis-[2,6-(di-tTo-propyl)phenyl]imidazol-2-ylidene) with gave the monomeric complex 3 [1], which was also obtained from the reaction of [RhCl(COE)(IPr)]2 2 with and excess IPr, while the reaction of [RhCl(COE)(lMes)]2 with gave the chloride bridged species 4 (Scheme 2.1) [2],... 

Early studies [170] of copper(II) complexes of thiosemicarbazones were 2-formylpyridine iV-methylthiosemicarbazone, 30, 6-methyl-2-formylpyridine Ai-methylthiosemicarbazone, 31, and 2-formylpyridine " JV-dimethylthiosemi-carbazone, 32. With copper(II) chloride and bromide, monomeric complexes of stoichiometry [Cu(L)A2] were isolated for each of these thiosemicarbazones. All six complexes had a band in the 14000-15000 cm spectral region, but their stereochemistry was not specified. 

Kitamura and Noyori have reported mechanistic studies on the highly diastere-omeric dialkylzinc addition to aryl aldehydes in the presence of (-)-i-exo-(dimethylamino)isoborneol (DAIB) [33]. They stated that DAIB (a chiral (i-amino alcohol) formed a dimeric complex 57 with dialkylzinc. The dimeric complex is not reactive toward aldehydes but a monomeric complex 58, which exists through equilibrium with the dimer 57, reacts with aldehydes via bimetallic complex 59. The initially formed adduct 60 is transformed into tetramer 61 by reaction with either dialkylzinc or aldehydes and regenerates active intermediates. The high enantiomeric excess is attributed to the facial selectivity achieved by clear steric differentiation of complex 59, as shown in Scheme 1.22. 

We report here studies on a polymer fi1m which is formed by the thermal polymerization of a monomeric complex tris(5,5 -bis[(3-acrylvl-l-propoxy)carbonyll-2,2 -bipyridine)ruthenium(11) as its tosylate salt,I (4). Polymer films formed from I (poly-I) are insoluble in all solvents tested and possess extremely good chemical and electrochemical stability. Depending on the formal oxidation state of the ruthenium sites in poly-I the material can either act as a redox conductor or as an electronic (ohmic) conductor having a specific conductivity which is semiconductorlike in magnitude. 

The N,S-chelate 2-aminoethanethiolate (aet-) forms stable cobalt(III) complexes, including clusters where the S can take on a bridging role. Reaction of [Co(NH3)5C1]2+ with Ni(aet)2 in water for several hours affords the black tetranuclear compound Co4(aet)8, which features act in simple chelate and bridging roles (245).1083 The simple monomeric complex [Co(aet)2(en)]+ has been reported 1084 when heated in water at 50 °C, the trimer Co Co(aet)3 2 is one product, with the central Co surrounded by six bridging S atoms. 

Nin-amido complexes such as (117) react with small electrophiles by insertion either in the Ni—N bond (e.g., with C02 to form (118)) or in the N—11 bond. With unsubstituted aryl groups (Ar = Ar = Ph), both a monomeric complex (117) or a dimeric species (119) is formed, depending on the amount of PMe3 added. Using bulky borylamide ligands, an almost linear, two-coordinate Nin complex could be obtained and structurally characterized.467 The N—Ni—N angle in (120) is 167.9°. 

Treatment with additional ligands like CN leads to monomeric complexes. Reaction of dimeric bis [/i-(2-mercaptoethyl)(2-mercaptoethyl)methylaminato]nickel(II) with either 02 or H202 leads to the formation of a dimeric product, bis [/u-(2-sulfinatoethyl)(2-mercaptoethyl)methylaminato (2-)]nickel(II). The reaction is first order in [Ni] and proceeds at a very slow rate at 40 °C (L/2 = 7.8 days k= 1.0 x 10 6s under 1 atm of 02. 297 Also the monomeric species can be oxidized to the mono(sulfones).1298-1302 These /ran.v-di thiolates do not undergo successive 02 addition to yield the bis(sulfone) like in (455a), which demonstrates the deactivation of the thiolate by the trawx-sulfone.1303... 

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