A pentacene with a 144 degrees twist

9,10,11,20,21,22-Hexaphenyltetrabenzo[a,c,l,n]pentacene (1) was prepared by the reaction of 1,3-diphenylphenanthro[9,10-c]furan with the bisaryne equivalent generated from 1,2,4,5-tetrabromo-3,6-diphenylbenzene in the presence of n-butyllithium, followed by deoxygenation of the double adduct with low-valent titanium. The X-ray structure of 1 shows it to be the most highly twisted polycyclic aromatic hydrocarbon known, with an end-to-end twist of 143.6 degrees . Compound 1 was resolved by chromatography on a chiral support, and the pure enantiomers have specific rotations in excess of 7000 degrees , but the molecule racemizes slowly at 25 degrees C (t1/2 = 9.3 h, DeltaGrac = 23.8 kcal/mol).     

N-heterocyclic carbene tethered amido complexes of palladium and platinum

With a view to applications in bifunctional catalysis, a modular cross-coupling strategy has been used to prepare amine bis(imidazolium) salts (3a and 3b) and an amine mono(imidazolium) salt (6) as precursors to chelating amido-NHC ligands. Treating the pro-ligands 3 with 3 equivalents of the bulky base KHMDS and Pd(OAc)(2) or PtCl(2)(COD) gave the four amido bis(N-heterocyclic carbene) pincer complexes [CNC-R]M-I [M = Pd (7) or Pt (8); R = i-Pr (a) or n-Bu (b)], including the first examples of platinum complexes of a CNC ligand. The reaction of 7a with AgOTf in pyridine gave the cationic complex {[CNC-i-Pr]Pd-py}OTf (9a). Heating a mixture of amine mono(imidazolium) salt 6 with PdCl(2) or K(2)PtCl(4), K(2)CO(3) and KI in pyridine at 100 °C gave the complexes [C,NH]MI(2)py [M = Pd (10) or Pt (11)], in which the amine arm of the NHC ligand is not deprotonated and does not coordinate to the metal. For a solution of 10 in 1,4-dioxane, deprotonation of the amine occurred in a biphasic reaction with aqueous KOH at 40 °C, giving the dimeric amido complex {[C,N]Pd(μ-OH)}(2) (12). The more inert Pt analogue 11 was unreactive under the same conditions. Solid-state structures of the complexes 7a, 7b, 9a, 10, 11 and 12 have been determined by single crystal X-ray diffraction.     

Reaction of nitrilimines with 2-substituted aza-heterocycles. Synthesis of pyrrolo[1,2-a]pyridine and pyrimido[2,1-d]1,2,3,5- tetrazine

The reaction of nitrilimine 6a with ethyl pyridine-2-acetate (7) gave the corresponding pyrrolo[1,2-a]pyridine 8, while the reaction of 6b containing an ester moiety afforded the acyclic adduct 9. The reaction of 6a with 2-aminopyrimidine (10) gave the novel unexpected pyrimido[2,1-d]1,2,3,5-tetrazine 11. Acyclic adducts 16 and 17 were obtained from the reaction of 6b with 2-cyanomethylbenzimidazole (14) and 2-aminobenzimidazole (15), respectively.     

Rhodium-catalyzed dehydrocoupling of fluorinated phosphine-borane adducts: synthesis, characterization, and properties of cyclic and polymeric phosphinoboranes with electron-withdrawing substituents at phosphorus

The dehydrocoupling of the fluorinated secondary phosphine-borane adduct R2PH.BH3 (R = p-CF3C6H4) at 60 degrees C is catalyzed by the rhodium complex [{Rh(mu-Cl)(1,5-cod)}2] to give the four-membered chain R2PH-BH2-R2P-BH3. A mixture of the cyclic trimer [R2P-BH2]3 and tetramer [R2P-BH2]4 was obtained from the same reaction at a more elevated temperature of 100 degrees C. The analogous rhodium-catalyzed dehydrocoupling of the primary phosphine-borane adduct RPH2.BH3 at 60 degrees C gave the high molecular weight polyphosphinoborane polymer [RPH-BH2]n (Mw = 56,170, PDI = 1.67). The molecular weight was investigated by gel permeation chromatography and the compound characterized by multinuclear NMR spectroscopy. Interestingly, the electron-withdrawing fluorinated aryl substituents have an important influence on the reactivity as the dehydrocoupling process occurred efficiently at the mildest temperatures observed for phosphine-borane adducts to date. Thin films of polymeric [RPH-BH2]n (R = p-CF3C6H4) have also been shown to function as effective negative-tone resists towards electron beam (e-beam) lithography (EBL). The resultant patterned bars were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS).     

Chiral phosphine Lewis base catalyzed asymmetric aza-Baylis-Hillman reaction of N-sulfonated imines with methyl vinyl ketone and phenyl acrylate

In the aza-Baylis-Hillman reaction of N-sulfonated imines with methyl vinyl ketone (MVK) promoted by chiral phosphine Lewis base: (R)-2'-diphenylphosphanyl-[1,1']binaphthalenyl-2-ol (10 mol%), the aza-Baylis-Hillman adducts 1 were obtained in good yields with high ee (70-94% ee) at -30 degrees C in THF. In CH2Cl2 upon heating at 40 degrees C, the aza-Baylis-Hillman reaction of N-sulfonated imines with phenyl acrylate gave the adducts 2 in high yields (60-97%) with moderate ee (52-77%).     

Synthesis of highly branched sulfur-nitrogen heterocycles by cascade cycloadditions of [1,2]dithiolo[1,4]thiazines and [1,2]dithiolopyrroles

We report the synthesis of some new polysulfur-nitrogen heterocycles by cascade cycloadditions to readily available polycyclic 1,2-dithiole-3-thiones. Thus, treatment of bis[1,2]dithiolopyrrole dithione 1 with dimethyl acetylenedicarboxylate (DMAD) or dibenzoylacetylene (DBA) gave the 1:4 adducts 2a,b and 3a. On the other hand, cycloaddition of bis[1,2]dithiolo[1,4]thiazine dithiones 4a-d with the same dipolarophiles gave the 1:2, 1:3, or 1:4 adducts 5a-c, 6a, 7a, 8a, 9a, and 10a,c,d selectively in fair to high yields. Reaction conditions were crucial for achievement of selectivity in thermal reactions. Catalysis by scandium triflate was used in the reaction of 4a and 2 equiv of DMAD. Treatment of the [1,2]dithiolo[1,4]thiazine dithione 11 with DBA gave the 1:2, 1:3 (two isomers), and 1:4 adducts 12-14 and 15a-d selectively. Cyclic voltammetry of selected examples showed irreversible processes that were not influenced by peripheral groups bonded to the heterocyclic system.     

Diels-Alder reactions of 4-triflyloxy-2,6,6-trimethyl-2,4-cyclohexadienone. An expedient methodology for the synthesis of bicyclo[2.2.2]oct-5-en-2-ones and bicyclo[2.2.2]octa-5,7-dien-2-ones

The synthesis of 4-triflyloxy-2,6,6-trimethyl-2,4-cyclohexadienone (13), bicyclo[2.2.2]octenones 1a-j and 15a-j, and bicyclo[2.2.2]octadienones 2a-f, 6a-d, and 11a-f is described. The 2,4-cyclohexadienones 4 and 13 were used for the first time as nondimerizing and easily accessible alternatives to 2,6,6-trimethyl-2,4-cyclohexadienone 12 in Diels-Alder reactions with acetylene derivatives 5a-d to prepare the adducts 6a-d and 11a-e in excellent yields. Compounds 11a-d were initially prepared by the alcoholysis of 6a-d to afford bicyclo[2.2.2]octene-2,5-diones 7a-dfollowed by treatment of 7a-d with N-phenyltriflimide in the presence of LHMDS at -78 degrees C. Diels-Alder reaction of 13 with an acetylene equivalent, phenyl vinyl sulfoxide, was also studied. A detailed study of the Diels-Alder reactions of various olefinic dienophiles 14a-j with 13 has been carried out to furnish cycloadducts 15a-j in high yields. Reductive removal of triflyloxy group of vinyl triflates 11a-f and 15a-j was performed in the presence of [Pd(PPh(3))(2)Cl(2)-Bu(3)N-HCO(2)H] to obtain the desired bicyclo[2.2.2]octadienones 2a-f and bicyclo[2.2.2]octenones 1a-j, respectively, in good overall yields.     

Thermolysis,photolysis, and oxidation of an overcrowded 1,3,2-dithiastannetane derivative

Reactions of a sterically crowded 1,3,2-dithiastannetane derivative bearing 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (=Tbt) and 2,4,6-triisopropylphenyl (=Tip) groups on the tin atom are described. Both thermolysis and photolysis of the 1,3,2-dithiastannetane [Tbt(Tip)SnS₂CPh₂] resulted in the formation of products derived from the corresponding stannanethione [Tbt(Tip)Sn=S], while the oxidation reaction by m -chloroperbenzoic acid gave a novel tincontaining heterocyclic system, an 1,2,4,5-oxadithiastannolane derivative.     

Chemistry of phosphine-borane adducts at platinum centers: dehydrocoupling reactivity of Pt(II) dihydrides with P-H bonds

The reaction of the Pt(II) dihydride complex cis-[PtH2(dcype)](dcype = 1,2-bis(dicyclohexylphosphino)ethane) with the primary or secondary phosphine-borane adducts PhRPH x BH3(R = H, Ph) was found to exclusively afford the mono-substituted complexes cis-[PtH(PPhR x BH3)(dcype)](1: R = H; 2: R = Ph)via a dehydrocoupling reaction between Pt-H and P-H bonds. Similar reactivity was observed between the uncoordinated phosphines PhRPH (R = H, Ph) and cis-[PtH2(dcype)], which gave cis-[PtH(PPhR)(dcype)](4: R = H; 5: R = Ph). The complexes were characterized by 1H, 11B, 13C and 31P NMR spectroscopy, IR, MS and, in the case of 2, X-ray crystallography that confirmed the cis geometries. The di-substituted complex cis-[Pt(PhPH x BH3)2(dcype)](3) was prepared from the reaction of cis-[PtCl2(dcype)] with two equivalents of Li[PPhH x BH3]. This suggested that steric reasons alone cannot be used to explain the lack of reactivity with respect to a second dehydrocoupling reaction involving the remaining Pt-H bond in complexes 1, 2, 4 and 5.     

Practical synthesis of an open geodesic polyarene with a fullerene-type 6:6-double bond at the center: diindeno[1,2,3,4-defg;1',2',3',4'-mnop]chrysene

Diindeno[1,2,3,4-defg;1',2',3',4'-mnop]chrysene (1), the smallest possible alkene-centered C60 substructure with a curved pi-system, is obtained in 25-35% yield by flash vacuum pyrolysis of the twisted 1,1'-dibromobifluorenylidene (2) on a 100 mg scale at 1050 degrees C. At 1200 degrees C, the bowl-shaped hydrocarbon 1 rearranges to the planar isomer diindeno[5,6,7,1-defg;5',6',7',1'-lmnop]chrysene (14) by a double 5/6 ring-expansion/ring-contraction. X-ray crystallography establishes that the central carbon atoms of 1 are nearly 80% as pyramidalized as the carbon atoms of C60 (POAV angles = 9.0 degrees and 11.6 degrees for 1 and C60, respectively). A four-step synthesis has been developed to prepare the pyrolysis precursor (2) as a mixture of (E)- and (Z)-isomers in 39% overall yield from commercially available 9-fluorenone-1-carboxylic acid (10).     

Generation and trapping reaction of an efficient 1,2-dehydrocarborane precursor, phenyl[o-(trimethylsilyl)carboranyl]iodonium acetate

An efficient 1,2-dehydrocarborane precursor, phenyl[o-(trimethylsilyl)carboranyl]iodonium acetate, was readily prepared by reaction of [o-(trimethylsilyl)carboranyl]lithium and IPh(OAc)2. The facile 2+4 cycloaddition of with dienes such as anthracene, naphthalene, norborna-2,5-diene and 2,5-dimethylfuran gave high yields of the 1,2-dehydrocarborane adducts in the presence of a desilylating agent. The reaction of with a cyclic alkene and strained cycloalkynes afforded the adducts formed by the ene reaction and the 2+2 cycloaddition reaction. The reaction of with a bicyclopalladacycle yielded the cyclization product. The structures of compounds and were determined by single-crystal X-ray crystallography.     

A theoretical and experimental study on the Lewis acid-base adducts (P(4)E(3)).(BX(3)) (E = S, Se; X = Br, I) and (P(4)Se(3)).(NbCl(5))

The Lewis acid-base adducts (P(4)E(3)).(BX(3)) (E = S, Se; X = Br, I) and (P(4)Se(3)).(NbCl(5)) have been prepared and characterized by Raman, IR, and solid-state (31)P MAS NMR spectroscopy. Hybrid density functional calculations (B3LYP) have been carried out for both the apical and the basal (P(4)E(3)).(BX(3)) (E = S, Se; X = Br, I) adducts. The thermodynamics of all considered species has been discussed. In accordance with solid-state (31)P MAS NMR and vibrational data, the X-ray powder diffraction structures of (P(4)S(3)).(BBr(3)) [monoclinic, space group P2(1)/m (No. 11), a = 8.8854(1) A, b = 10.6164(2) A, c = 6.3682(1) A, beta = 108.912(1) degrees, V = 568.29(2) A(3), Z = 2] and (P(4)S(3)).(BI(3)) [orthorhombic, space group Pnma (No. 62), a = 12.5039(5) A, b = 11.3388(5) A, c = 8.9298(4) A, V = 1266.09(9) A(3), Z = 4] indicate the formation of an apical P(4)S(3) complex in the reaction of P(4)S(3) with BX(3) (X = Br, I). Basal adducts are formed when P(4)Se(3) is used as the donor species. Vibrational assignment for the normal modes of these adducts has been made on the basis of comparison between theoretically obtained and experimentally observed vibrational data.     

Homoleptic cadmium and mercury compounds of stanna-closo-dodecaborate

The reaction of stanna- closo-dodecaborate [SnB 11H 11] (2-) (1) with CdBr 2 gave the tetrahedrally coordinated compound [Cd(SnB 11H 11) 4] (6-)(2). The same coordination mode can be found in [Hg(SnB 11H 11) 4] (6-) (3), which was obtained by reaction of stannaborate with Hg 2Cl2. Both compounds were characterized by single crystal X-ray analysis and heteronuclear NMR techniques.     

Metal telluride clusters composed of niobocene carbonyl, telluride, and cobalt carbonyl units: syntheses, structures, and reactivity

Abstract: The reaction of [Cp#2NbTe2H] (1#; Cp# = Cp* (C5Me5) or Cp(x) (C5Me4Et)) with two equivalents of [Co2(CO)8] gives a series of cobalt carbonyl telluride clusters that contain different types of niobocene carbonyl fragments. At 0 degrees C, [Cp#2NbTe2CO3(CO)7] (2#) and [Co4Te2(CO)10] (3) are formed which disappear at higher temperatures: in boiling toluene a mixture of [cat2][Co9Te6(CO)8] (5#) (cat= [Cp#2Nb(CO)2]+) and [cat2][Co11Te7(CO)10] (6#) is formed along with [cat][Co(CO)4] (4#). Complexes 6# transform into [cat][Co11Te7(CO)10] (7#) upon interaction with HPF6 or wet SiO2. The molecular structures of 2(Cp(x)), 4(Cp(x)), 5(Cp*), 6(Cp*) and 7(Cp*) have been determined by X-ray crystallography. The structure of the neutral 2(Cp(x)) consists of a [Co3(CO)6Te2] bipyramid which is connected to a [(C5Me4Et)2Nb(CO)] fragment through a mu4-Te bridge. The ionic structures of 4(Cp(x)), 5(Cp*), 6(Cp*) and 7(Cp*) each contain one (4, 7) or two (5, 6) [Cp#2Nb(CO)2]+ cations. Apart from 4, the anionic counterparts each contain an interstitial Co atom and are hexacapped cubic cluster anions [Co9Te6(CO)8]2- (5) or heptacapped pentagonal prismatic cluster anions [Co11Te7(CO)10]n- (n=2: [6]2- , n=1: [7]-), respectively. Electrochemical studies established a reversible electron transfer between the anionic clusters [Co11,Te7(CO)10]- and [Co11Te7(CO)10]2in 6# and 7# and provided evidence for the existence of species containing [Co11Te7(CO),0] and [Co11Te7(CO)0]3-. The electronic structures of the new clusters and their relative stabilities are examined by means of DFT calculations.     

Reaction of thioketones with propiolic acids

The reaction of adamantane-2-thione with propiolic acid afforded a novel type of cycloadduct, spiro[adamantane-2,2'-6'H-[1,3]-oxathiin]-6'-one (3a), in quantitative yield. The reaction of thiobenzophenone with propiolic acid gave 2,2-diphenyl-6'H-[1,3]-oxathiin]-6'-one and 4-phenyl-3-thia-3,4-dihydronaphthoic acid in 34% and 35% yields, respectively. The reaction might proceed through a concerted process, as confirmed by kinetics. The reaction of adamantane-2-thione with 2-butynoic acid or phenylpropiolic acid gave the corresponding adducts regioselectively. Interestingly, only one isomer was obtained by the reaction of thiofenchone with propiolic acid, suggesting that the reaction proceeded diastereospecifically. Oxidation of adducts by dimethyldioxirane or m-chloroperoxybenzoic acid gave the corresponding sulfoxides and sulfones. The sulfoxides were thermally decomposed to give disulfide or another type of 1,3-oxathiin-6-one.     

Cyclization of electron-deficient cyclopentadienone with 2-alkenyl and 2-alkynylamines via sequential pericyclic reaction pathway.

The pericyclic reactions of 2,5-bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone (1a) with both allylic and propargylic amines have been investigated. The reaction proceeded via initial formation of the 1,4 adducts followed by the ene cyclization and/or sequential pericyclic reactions depending upon the structures of the amines. The reaction of 1a with diallylamine (2a) gave the tetracyclic compound (3a). On the other hand, the reaction of 1a with 2-propynylamine (2c) gave exclusively the bicyclic compound (5c). In the reactions with the secondary 2-propynylamines (2d,e), the tetracyclic compounds (3d,e) were exclusively formed. The reactions of 1a with alpha-branched primary 1,1-dialkyl-2-propynylamines (2f,g) gave mixtures of 3- and 5-type compounds. The tetracyclic compounds 3 were formed from the intramolecular [4+2]pi cycloadditions of the [1,5]-sigmatropic rearrangement products of the 1,4 adducts of 1a and 2, followed by the [1,5]-sigmatropic rearrangement of hydrogen and dehydrogenation. The bicyclic compounds 5 were derived from the [2pi+2pi+2sigma] reaction of the 1,4 adducts of 1a and 2. The one-pot multistage sequential pericyclic reactions were discussed on the basis of the X-ray crystallographic structures and the MO calculation data.     

Formation of a novel trinuclear spirostannoxane tin(IV) compound. Crystal and molecular structure of [Sn(nBu)(Cl)[(OCH2CH2S)2Sn(nBu)]2] and the stannolane [(nBu)Sn(SCH2CH2O)SCH2CH2OH

The reaction of nBuSnCl3 and the sodium salt of 2-mercaptoethanol (1:1) in ethanol gave the compound Sn(nBu)(Cl)[(OCH2CH2S)2Sn(nBu)]2 (1). [(nBu)Sn(SCH2CH2O)SCH2CH2OH] (2) was initially isolated from the reaction of 1 with nBuMgCl as a rearrangement product but was also synthesized from nBuSn(O)OH and two molar equivalents of 2-mercaptoethanol. Both compounds were characterized by means of IR, 119Sn, 13C, and 1H NMR, FAB mass spectroscopy, and elemental analyses. The structures were determined by single-crystal X-ray diffraction. 1 crystallizes in the monoclinic Cc space group (a = 18.492(3) A, b = 17.329(2) A, c = 10.787(1) A, beta = 111.88(1) degrees, Z = 4), while 2 crystallizes in the orthorhombic Pbca space group (a = 14.458(2) A, b = 10.393(1) A, c = 16.479(2) A, Z = 8). 1 is a trimetallic Tin(IV) compound in which the central atom is in 6-fold coordination, while the two remaining tin atoms show 5-fold coordination. Both pentacoordinated tin atoms are bonded to a butyl group and to the oxygen and the sulfur atoms from two [OCH2CH2S]2- ligands forming two stannolanes, which are fused with the hexacoordinated tin atom forming a distannoxane system. This arrangement is quite different from previous ladder or staircase structures. NMR data point to maintenance of this structure in solution. 2 consists of [(nBu)Sn(SCH2CH2O)(SCH2CH2OH)] units, which are associated via intermolecular Sn-O interactions building up a dimer. The tin atom forms two "stannolane" units by interaction with [OCH2CH2S]2- and [HOCH2CH2S]- ligands.     

Configurationally stable longitudinally twisted polycyclic aromatic compounds

Two strategies for the synthesis of configurationally stable twisted polycyclic aromatic compounds (PACs) were pursued. The first approach employed dissymmetrically positioned 1-naphthyl substituents to bias the direction of twist in highly substituted PACs. 2,3-Bis(1-naphthyl)-1,4-diphenyltriphenylene (7) was prepared, and its meso cis-dinaphthyl and enantiomeric trans-dinaphthyl isomers were resolved by preparative supercritical fluid chromatography (SFC) on chiral supports. Similarly, several naphthyl-substituted derivatives of the more highly twisted 9,10,11,12,13,14-hexaphenylbenzo[b]triphenylene (2) were prepared. Of these, 10-(1-naphthyl)-9,11,12,14-tetraphenylbenzo[b]triphenylene (13) was resolved by SFC on a chiral support. The pure enantiomers of trans-7 showed moderately large specific rotations ([alpha]D(25) = -330 and +320 degrees), but the specific rotations for the enantiomers of 13 were unexpectedly small ([alpha]D(25) = -23 and +23 degrees). Computational studies suggest that the latter result is due to presence of a minor conformation of 13 possessing a larger rotation of opposite sign than the major conformation. Both 7 and 13 showed strong circular dichroism and moderately strong circularly polarized luminescence. A byproduct of these syntheses was 9,10,19,21-tetraphenyldiphenanthro[9,10-b:9,10-h]carbazole (15), a very crowded carbazole that exhibits an 81 degree end-to-end twist but is not resolvable. In the second approach, the large, twisted, polycyclic aromatic ligand 9,10,11,12,13,14-hexaphenylbenzo[h]naphtho[2,3-f]quinoline (21, an aza-2) was used to prepare the chiral, cyclometallated iridium(III) complex 4. The ligand 21 was prepared via an unusually stable benzannulated norbornadienone, for which the free energy of activation for decarbonylation was a remarkable 33.5 kcal/mol. The iridium complex 4 proved to be configurationally stable and resolvable by analytical HPLC on chiral supports, but the low solubility of 4 prevented its resolution on a preparative scale. A much more soluble dibutyl analogue of 4 (complex 28) was then prepared, but it was not resolvable on any of the available media.     

Chloromethanesulfonylethene and dichloromethanesulfonylethene: new reagents for tandem Diels-Alder/Ramberg-Bäcklund reactions

[reaction: see text] Chloromethanesulfonylethene (3a) and dichloromethanesulfonylethene (3b) were prepared by oxidation of the adducts of ethylene and ClCH(2)SCl or Cl(2)CHSCl, respectively, followed by NaHCO(3) dehydrochlorination. With dienes, 3a gave Diels-Alder adducts that, with base, underwent Ramberg-B?cklund reaction, giving products corresponding to the adducts of the dienes and allene. Similarly, 3b gave Diels-Alder adducts that, with base in the presence of the novel chlorine source MeSO(2)CCl(3), cleanly afforded products corresponding to the adducts of the dienes and 1,1-dichloropropa-1,2-diene.     

Kinetics and mechanism for reversible chloride transfer between mercury(II) and square-planar platinum(II) chloro ammine, aqua, and sulfoxide complexes. Stabilities, spectra, and reactivities of transient metal-metal bonded platinum-mercury adducts

The Hg2+aq- and HgCl+aq-assisted aquations of [PtCl4]2- (1), [PtCl3(H2O)]- (2), cis-[PtCl2(H2O)2] (3), trans-[PtCl2(H2O)2] (4), [PtCl(H2O)3]+ (5), [PtCl3Me2SO]- (6), trans-[PtCl2(H2O)Me2SO] (7), cis-[PtCl(H2O)2Me2SO]+ (8), trans-[PtCl(H2O)2M32SO]+ (9), trans-[PtCl2(NH3)2] (10), and cis-[PtCl2(NH3)2] (11) have been studied at 25.0 degrees C in a 1.00 M HClO4 medium buffered with chloride, using stopped-flow and conventional spectrophotometry. Saturation kinetics and instantaneous, large UV/vis spectral changes on mixing solutions of platinum complex and mercury are ascribed to formation of transient adducts between Hg2+ and several of the platinum complexes. Depending on the limiting rate constants, these adducts are observed for a few milliseconds to a few minutes. Thermodynamic and kinetics data together with the UV/vis spectral changes and DFT calculations indicate that their structures are characterized by axial coordination of Hg to Pt with remarkably short metal-metal bonds. Stability constants for the Hg2+ adducts with complexes 1-6, 10, and 11 are (2.1 +/- 0.4) x 10(4), (8 +/- 1) x 10(2), 94 +/- 6, 13 +/- 2, 5 +/- 2, 60 +/- 6, 387 +/- 2, and 190 +/- 3 M-1, respectively, whereas adduct formation with the sulfoxide complexes 7-9 is too weak to be observed. For analogous platinum(II) complexes, the stabilities of the Pt-Hg adducts increase in the order sulfoxide < aqua < ammine complex, reflecting a sensitivity to the pi-acid strength of the Pt ligands. Rate constants for chloride transfer from HgCl+ and HgCl2 to complexes 1-11 have been determined. Second-order rate constants for activation by Hg2+ are practically the same as those for activation by HgCl+ for each of the platinum complexes studied, yet resolved contributions for Hg2+ and HgCl+ reveal that the latter does not form dinuclear adducts of any significant stability. The overall experimental evidence is consistent with a mechanism in which the accumulated Pt(II)-Hg2+ adducts are not reactive intermediates along the reaction coordinate. The aquation process occurs via weaker Pt-Cl-Hg or Pt-Cl-HgCl bridged complexes.