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Sterically constrained tricyclic phosphine: redox behaviour, reductive and oxidative cleavage of P-C bonds, generation of a dilithium phosphaindole as a promising synthon in phosphine chemistry.

ABSTRACT: The redox behaviour of sterically constrained tricyclic phosphine 3a was investigated by spectroelectrochemistry. The data suggested a highly negative reduction potential with the reversible formation of a dianionic species. Accordingly, 3a reacted with two equivalents of Li/naphthalene by reductive cleavage of a P-C bond of one of the PC₄ heterocycles. The resulting dilithium compound 5 represents a phosphaindole derivative with annulated aromatic C₆ and PC₄ rings. It is an interesting starting material for the synthesis of new heterocyclic molecules, as was shown by treatment with Me₂SiCl₂ and PhPCl₂. The structures of the products (6 and 7) formally reflect ring expansion by insertion of silylen or phosphinidene fragments into a P-C bond of 3a. Treatment of 3a with H₂O₂ did not result in the usually observed transfer of a single O atom to phosphorus, but oxidative cleavage of a strained PC₄ ring afforded a bicyclic phosphinic acid, R₂PO₂H.

SUBMITTER: Brand A

PROVIDER: S-EPMC8179454 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Adaptive responses of sterically confined intramolecular chalcogen bonds.

Project description:The responsive behavior of an entity towards its immediate surrounding is referred to as an adaptive response. The adaptive responses of a noncovalent interaction at the molecular scale are reflected from its structural and functional roles. Intramolecular chalcogen bonding (IChB), an attractive interaction between a heavy chalcogen E (E = Se or Te) centered sigma hole and an ortho-heteroatom Lewis base donor D (D = O or N), plays an adaptive role in defining the structure and reactivity of arylchalcogen compounds. In this perspective, we describe the adaptive roles of a chalcogen centered Lewis acid sigma hole and a proximal Lewis base (O or N) in accommodating built-in steric stress in 2,6-disubstituted arylchalcogen compounds. From our perspective, the IChB components (a sigma hole and the proximal Lewis base) act in synergism to accommodate the overwhelming steric force. The adaptive responses of the IChB components are inferred from the observed molecular structures and reactivity. These include (a) adaptation of a conformation without IChBs, (b) adaptation of a conformation with weak IChBs, (c) twisting the skeletal aryl ring while maintaining IChBs, (d) ionization of the E-X bond (e.g., X = Br) to relieve stress and (e) intramolecular cyclization to relieve steric stress. A comprehensive approach, involving X-ray data analysis, density functional theory (DFT) calculations, reaction pattern analysis and principal component analysis (PCA), has been employed to rationalize the adaptive behaviors of IChBs in arylchalcogen compounds. We believe that the perception of ChB as an adaptive/stimulus responsive interaction would profit the futuristic approaches that would utilise ChB as self-assembly and molecular recognition tools.

| S-EPMC6137456 | biostudies-literature

Isolable Geminal Bisgermenolates: A New Synthon in Organometallic Chemistry.

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| S-EPMC8596710 | biostudies-literature

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Project description:Tris(2-(trimethylsilyl)phenyl)phosphine, P(o-TMSC6 H4 )3 , was synthesised and characterised in solution and in the solid state. The large steric bulk prevents most reactions of the phosphorus donor and makes the compound air stable both in the solid state as well as in solution. This shielded phosphine can still undergo three reactions, namely protonation, oxidation to the phosphine oxide under harsh conditions and complexation to AuI , thus forming a complex with linear coordination. Unexpectedly, complexation was unsuccessful with a range of other metal cations. Neither PdII , PtII , ZnII nor HgII reacted and even the remaining coinage metal cations CuI and AgI could not be coordinated. Both the parent molecule as well as the reaction products were structurally characterised by single crystal X-ray diffraction, and the conformational change of geometry required to accommodate the additional atoms was analysed in detail. Apart from chemical oxidation with H2 O2 , P(o-TMSC6 H4 )3 displays reversible electrochemical oxidation with a potential not unlike the one of sterically unencumbered phosphines for which the oxidation is usually not reversible. P(o-TMSC6 H4 )3 can thus be considered a model compound for the investigation of the electronic properties of sterically unencumbered phosphines.

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Project description:A geometrically constrained phosphine bearing a tridentate NNS pincer ligand is reported. The effect of the geometric constraint on the electronic structure was probed by theoretical calculations and derivatization reactions. Reactions with N-H bonds result in formation of cooperative addition products. The thermochemistry of these transformations is strongly dependent on the substrate, with ammonia activation being thermoneutral. This represents the first example of a molecular compound that reversibly activates ammonia via N-H bond scission in solution upon mild heating.

| S-EPMC8596738 | biostudies-literature

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| S-EPMC5707506 | biostudies-literature

Phosphine-catalyzed formation of carbon-sulfur bonds: catalytic asymmetric synthesis of gamma-thioesters.

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| S-EPMC2850260 | biostudies-literature

Sterically controlled reductive oligomerisations of CO by activated magnesium(i) compounds: deltate <i>vs.</i> ethenediolate formation.

Project description:An extremely bulky, symmetrical three-coordinate magnesium(i) complex, [{(TCHPNacnac)Mg}2] (TCHPNacnac = [{(TCHP)NCMe}2CH]-, TCHP = 2,4,6-tricyclohexylphenyl) has been prepared and shown to have an extremely long Mg-Mg bond (3.021(1) Å) for such a complex. It was shown not to react with either DMAP (4-dimethylaminopyridine) or CO. Three unsymmetrical 1 : 1 DMAP adducts of less bulky Mg-Mg bonded species have been prepared, viz. [(ArNacnac)Mg-Mg(DMAP)(ArNacnac)] (ArNacnac = [(ArNCMe)2CH]- Ar = 2,6-xylyl (Xyl), mesityl (Mes) or 2,6-diethylphenyl (Dep)), and their reactivity toward CO explored. Like the previously reported bulkier complex, [(DipNacnac)Mg-Mg(DMAP)(DipNacnac)] (Dip = 2,6-diisopropylphenyl), [(DepNacnac)Mg-Mg(DMAP)(DepNacnac)] reductively trimerises CO to give a rare example of a deltate complex, [{(DepNacnac)Mg(μ-C3O3)Mg(DMAP)(DepNacnac)}2]. In contrast, the two smaller adduct complexes react with only two CO molecules, ultimately giving unusual ethenediolate complexes [{(ArNacnac)Mg{μ-OC(H)[double bond, length as m-dash]C(DMAP-H)O}Mg(ArNacnac)}2] (Ar = Xyl or Mes). DFT calculations show the latter reactions to proceed via reductive dimerizations of CO, and subsequent intramolecular C-H activation of Mg-ligated DMAP by "zig-zag" [C2O2]2- fragments of reaction intermediates. Calculations also suggest that magnesium deltate complexes are kinetic products in these reactions, while the magnesium ethenediolates are thermodynamic products. This study shows that subtle changes to the bulk of the reacting 1 : 1 DMAP-magnesium(i) adduct complexes can lead to fine steric control over the products arising from their CO reductive oligomerisations. Furthermore, it is found that the more activated nature of the adduct complexes, relative to their symmetrical, three-coordinate counterparts, [{(ArNacnac)Mg}2], likely derives more from the polarisation of the Mg-Mg bonds of the former, than the elongated nature of those bonds.

| S-EPMC8152598 | biostudies-literature

Three-centre hydrogen bonds in triphenyl-phosphine oxide-hydro-quinone (1/1).

Project description:The title cocrystal, C(18)H(15)OP·C(6)H(6)O(2), belongs to a series of mol-ecular systems based on triphenyl-phosphine P-oxide. The O atom of the oxide group acts as an acceptor for hydrogen bonds from OH groups of two hydro-quinone mol-ecules which lie on inversion centres [O?O = 2.7451?(17) and 2.681?(2)?Å]. The crystal structure is stabilized by weak C-H?O hydrogen bonds, forming a C(2) (1)(8) chain which runs parallel to the [100] direction.

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Biaryl Phosphine Based Pd(II) Amido Complexes: The Effect of Ligand Structure on Reductive Elimination.

Project description:Kinetic studies conducted under both catalytic and stoichiometric conditions were employed to investigate the reductive elimination of RuPhos (2-dicyclohexylphosphino-2',6'-diisopropoxybiphenyl) based palladium amido complexes. These complexes were found to be the resting state in Pd-catalyzed cross-coupling reactions for a range of aryl halides and diarylamines. Hammett plots demonstrated that Pd(II) amido complexes derived from electron-deficient aryl halides or electron-rich diarylamines undergo faster rates of reductive elimination. A Hammett study employing SPhos (2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl) and analogues of SPhos demonstrated that electron donation of the "lower" aryl group is key to the stability of the amido complex with respect to reductive elimination. The rate of reductive elimination of an amido complex based on a BrettPhos-RuPhos hybrid ligand (2-(dicyclohexylphosphino)-3,6-dimethoxy-2',6'-diisopropoxybiphenyl) demonstrated that the presence of the 3-methoxy substituent on the "upper" ring of the ligand slows the rate of reductive elimination. These studies indicate that reductive elimination occurs readily for more nucleophilic amines such as N-alkyl anilines, N,N-dialkyl amines, and primary aliphatic amines using this class of ligands.

| S-EPMC5127253 | biostudies-literature

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