Comparison of Phosphorus and Silicon: Hypervalency, Stereochemistry, and Reactivity

P-O donor action from carboxylate anions with phosphorus in the presence of hydrogen bonding. A model for phosphoryl-transfer enzymes

A series of phosphorus compounds (1-3) containing anionic carboxylate groups were synthesized by treatment of the respective neutral precursor acid forms B-D with amines, which also served to introduce hydrogen-bonding interactions. The compounds, subjected to X-ray structure analysis, resulted in hexacoordinated anionic phosphoranates 1A and 1B, a pseudo-trigonal-bipyramidal anionic phosphine (2), and a trigonal-bipyramidal anionic phosphine oxide (3). The structures revealed that P-O donor coordination was present in all members of the anionic series 1-3 and resulted in stronger interactions than existed in the precursor neutral acid forms B-D as measured by the presence of shorter P-O distances. Evaluation of the energies of the donor interactions relative to the energies of the hydrogen bonds that were present showed that the donor energies now exceeded the hydrogen bond strengths. (31)P chemical shifts indicated that the basic coordination geometries were retained in solution. Both 1A and 1B are chiral and exist as racemates. The results suggest that mechanisms of phosphoryl-transfer enzymes should benefit by taking into account donor interactions at phosphorus by residues at active sites in addition to the inclusion of hydrogen bonding. Reference is made to specific phosphoryl-transfer enzymes.

Coordination of carbonyl and carboxyl oxygen atoms with phosphorus in the presence of hydrogen bonding. P-O donor action

A series of phosphorus compounds 1-5 containing carbonyl or carboxyl groups was obtained and subjected to X-ray analysis. Syntheses of the phosphoranes 1 and 5 were effected by oxidation reactions using potassium permaganate, while the phosphine oxide 2 was obtained by oxidation with hydrogen peroxide. The readily available phosphines 3 and 4 were included in the study. The structures revealed that P-O coordination occurred for 1-3 in the presence of extensive hydrogen bonding and led to trigonal bipyramidal geometries. A similar structure was observed for 4 in the absence of hydrogen bonding. (31)P chemical shifts indicate retention of the basic coordination geometries in solution. Consideration of the chirality of the phosphoranes 1 and 5 leads to a pair of mirror images that are possible in solution but exist in preferred isomeric forms in the crystalline state. Evaluation of the energies of two competing bonding types indicated a range for P-O coordination above and below the hydrogen bond energy. The results suggest that phosphoryl transfer enzyme mechanisms should benefit by taking into account donor interactions to phosphorus by residues at active sites in addition to the inclusion of hydrogen bonding interactions.

Monocyclic Zwitterionic λ5Si-Silicates with an SiO2FC2 Framework: Syntheses and Structural Characterization in the Solid State and in Solution

Treatment of the acyclic zwitterionic pentacoordinate silicate F(3)MeSiCH(2)NMe(2)H with 1 molar equiv of Me(3)SiOC(6)H(4)OSiMe(3), Me(3)SiOCH(2)C(O)OSiMe(3), Me(3)SiOC(Ph)=NOSiMe(3), or Me(3)SiOC(O)C(O)OSiMe(3) (solvent CH(3)CN, room temperature) yielded the respective monocyclic zwitterionic pentacoordinate silicates (11a), (12a), (13a), and (14a), along with 2 molar equiv of Me(3)SiF. The derivatives 11b-14b with a 2,2,6,6-tetramethylpiperidinio substituent instead of the dimethylammonio group were prepared analogously, starting from F(3)MeSiCH(2)NR(2)H (NR(2)H = 2,2,6,6-tetramethylpiperidinio). Single-crystal X-ray diffraction studies showed that the Si-coordination polyhedra of 11a.1.5CH(3)CN, 12a-14a, and 11b-14b are distorted trigonal bipyramids, the axial positions being occupied by the fluorine atom and one of the two oxygen atoms (12a/12b, carboxylate oxygen atom; 13a/13b, carbon-linked oxygen atom). These results are in agreement with the NMR data ((1)H, (13)C, (19)F, (29)Si) obtained for these compounds in solution. The chiral (C(1) symmetry) zwitterions 11a-14a and 11b-14b exist as pairs of (A)- and (C)-enantiomers in solution. VT (1)H NMR studies with 11b-14b in CH(3)CN in the temperature range 25-85 degrees C gave no indications for an enantiomerization process [(A)/(C)-enantiomerization] at the silicon atom.

A Novel Type of Nucleophilic Substitution Reactions on Nonactivated Aromatic Compounds and Benzene Itself with Trimethylsiliconide Anions

[reaction: see text]. The reaction of fluorobenzene with Me3Si- anion (1) in HMPA at room temperature surprisingly affords o- and p-fluorotrimethylsilylbenzenes (substitution of aromatic H for TMS, 76% yield) 7a and 7b and also 14% of trimethylsilylbenzene (2). Benzene itself reacts at 50 degrees C to furnish 4 in 45% yield. Pyridine affords p-trimethylsilylpyridine quantitatively. Mechanistic studies are presented.

Synthesis and structure of cyclic phosphate, phosphoramidate, phosphonates, and phosphonium salts. Phosphatrane formation

Reaction of tris(2-hydroxy-3,5-dimethylbenzyl)amine (6) with phosphorus reagents led to the formation of the phosphoramidate, N[CH2(Me2C6H2)O]2PO (1), the phosphate N[CH2(Me2C6H2)O]2[CH2(Me2C6H2)OH]P(O)(OPh) (2), the phosphonium salts N[CH2(Me2C6H2)O]3PMe+I- (3A) and N[CH2(Me2C6H2)O]3PMe+I3- (3B), and the phosphonates N[CH2(Me2C6H2)O]2[CH2(Me2C6H2)OH]P(O)Me (4) and N[CH2(Me2C6H2)O]2[CH2(Me2C6H2)OSiMe3]P(O)Me (5). X-ray analysis provided molecular structures for all of the compounds. The solid-state structural representations were supported in solution by an analysis of the NCH2 proton NMR patterns. The structures of 3A and 3B show the presence of phosphatranes with weak P-N donor interactions. These represent the first phosphatranes containing all six-membered rings. Variable temperature analysis of the 1H NMR spectra of 3A indicates fluxional behavior whereby a racemic mixture of the chiral phosphonium salt rapidly intraconverts at room temperature. The activation energy for the enantiomeric conversion of the clockwise and anticlockwise orientations of the propeller-like phosphatrane is 11.2 kcal/mol, which is compared to that of the isoelectronic silatrane N[CH2(Me2C6H2)O]3SiMe (E), 10.3 kcal/mol.

Preparation of hexacoordinated tris(bidentate) phosphorus compounds with 1,3,2-dioxaphosphorinane rings. NMR and X-ray crystallographic studies of their conformation

A series of new unstable tris(bidentate) hexacoordinated phosphorus compounds 1 with 1,3,2-dioxaphosphorinane rings was prepared and studied by NMR and X-ray crystallography. The X-ray crystal structures showed that the 1,3,2-dioxaphosphorinane ring adopts different conformations depending on the number and size of substituents at the carbon atom C14. Substituents are deployed around the phosphorus atom in a slightly deformed octahedral structure. Deviations in bond lengths around the phosphorus atom depend on the character of the bonds and the distribution of the negative charge. (1)H and (13)C NMR measurements showed that in solution the flexibility of 1,3,2-dioxaphosphorinane ring depends on the size of substituents at the carbon C14.

Evidence for Nondissociative Ligand Exchange within [4+2]-Coordinate Phosphorus Species in Solution

[4+2]-Coordinate phosphorus compounds, [bis(8-(dimethylamino)-1-naphthyl)]phenylphosphane, [bis(8-(dimethylamino)-1-naphthyl)]phenylphosphane sulfide, [bis(8-(dimethylamino)-1-naphthyl)]phenylphosphonium bromide, [bis(8-(dimethylamino)-1-naphthyl)]methylphosphane, and [bis(8-(dimethylamino)-1-naphthyl)]phosphane oxide, with two identical bidentate (8-(dimethylamino)-1-naphthyl) ligands have asymmetrical geometries in solution and undergo intramolecular nondissociative ligand exchange as shown by dynamic (1)H NMR studies. The DeltaG() values for this process were found to lie in the range 56.2-61.7 kJ mol(-)(1). The (1)H NMR study for bis[(8-(dimethylamino)-1-naphthyl)]phenylphosphane sulfide has revealed that two hexacoordinate isomers coexist in solution in a solvent dependent ratio. Their interconversion in solution is consistent with an intramolecular 1,2-shift of adjacent ligands.

Synthesis of Phosphoramides for the Lewis Base-Catalyzed Allylation and Aldol Addition Reactions

Both chiral and achiral phosphoramides of diverse structure were prepared from diamines by the coupling to phosphorus(V) or phosphorus(III) reagents. Several enantiopure 1,2-diphenyl-1,2-ethanediamine analogues have been prepared by the reductive coupling of the corresponding N-silylimine with NbCl(4)(THF)(2) and subsequent resolution by the formation of diastereomeric menthyl carbamates. (S,S)-N,N'-Di-(1-naphthyl)-1,2-diphenyl-1,2-ethanediamine 15 was prepared by the arylation of (S,S)-1,2-diphenyl-1,2-ethanediamine with naphthyl iodide.

Complexes of Multifunctional Phosphorus Ligands. Rhenium(V) Complexes of the Multidentate Phenoxyphosphine Ligands Bis(o-trimethylsilyloxyphenyl)phenylphosphine and Tris(o-trimethylsilyloxyphenyl)phosphine. Stepwise Elimination of Me(3)SiX (X = Cl, OEt) from the Metal-Ligand System

The silylated aryloxo ligands bis(o-silyloxyphenyl)phenylphosphine (abbreviated PhP{OT}(2)) and tris(o-trimethylsilyloxyphenyl)phosphine (abbreviated P{OT}(3), where T = Me(3)Si) were prepared. Complexation reactions with O=ReCl(2)(OEt)(PPh(3))(2) and O=ReCl(3)(PPh(3))(2) proceed by displacement of one PPh(3) and the subsequent stepwise replacement of the OEt and/or Cl substituents. The new complex Re(O)Cl(2)[kappa(2)-(P,O)-(PhP{O}{OT})](PPh(3)), formed by elimination of Me(3)SiOEt, exists in diastereomeric cis and trans forms. Elimination of a second equivalent of Me(3)SiCl gives Re(O)Cl[kappa(3)-(P,O,O)-(PhP{O}(2))](PPh(3)). Similarly P{OT}(3) converts Re(O)Cl(2)(OEt)(PPh(3))(2) to ReOCl(2)[kappa(2)-(P,O)-(P{O}{OT}(2))](PPh(3)) (5) (structurally characterized as 5.0.875CH(2)Cl(2)): crystal data; triclinic P&onemacr;, a = 14.302(4) Å, b = 18.734(2) Å, c = 17.639(4) Å, alpha = 80.950(12) degrees, beta = 80.12(2) degrees, gamma = 81.76(2) degrees, Z = 4. Final R(1) and wR(2) values are 0.0852 and 0.1525, respectively on F(o)(2) > 2sigma(F(o)(2)) data (or 0.1948 and 0.2019 on all data). The phenoxy phosphine ligand in 5 is bound via P and one O to Re. The P atoms are mutually cis to each other and to the terminal oxygen on Re. Two ortho-trimethylsiloxy substituted phenyl rings dangle from the coordinated phosphorus atom. Complex 5 can be converted to Re(O)Cl[kappa(3)-(P,O,O)-(P{O}(2){OT})](PPh(3)) (6) by treatment with PPN(+) Cl(-) and 6 was also obtained by direct reaction of Re(O)Cl(3)(PPh(3))(2) with P{OT}(3) at higher temperatures. The complex 6 has been structurally characterized: crystal data triclinic, P&onemacr;, a = 10.1509(6) Å, b = 12.1123(8) Å, c = 16.2142(14) Å, alpha = 97.851(7) degrees, beta = 94.852(7) degrees, gamma = 96.889(6) degrees, Z = 2. Final R(1) and wR(2) values were 0.0303 and 0.0721 on F(o)(2) > 2sigma(F(o)(2)) data (or 0.0348 and 0.0742 on all data). The phenoxyphosphine ligand in 6 is bound facially to Re through P and two of the phenoxy oxygens. The Ph(3)P group and terminal oxygen atoms are cis to the oxygen atoms of the phenoxy ligands and the Cl lies trans to P. One trimethylsiloxyphenol group dangles. Careful hydrolysis of 6 gave Re(O)Cl[kappa(3)-(P,O,O)-(P{O}(2){OH})](PPh(3)) which was also formed during complexation reactions in moist solvent. Solution (31)P{(1)H} NMR demonstrated cis- or trans-(P,P) geometry for the complexes, which was confirmed in the two aforementioned cases by structure determinations.