5666-12-6Relevant articles and documents
Synthesis of electron-rich sterically hindered P1 phosphazene bases by the staudinger reaction
Alexandrova, Anastasia V.,Masek, Tomas,Polyakova, Svetlana M.,Cisarova, Ivana,Saame, Jaan,Leito, Ivo,Lyapkalo, Ilya M.
, p. 1811 - 1823 (2013/04/10)
The synthesis of electron-rich P1 phosphazene bases with a sterically protected basic center by a Staudinger reaction is reported. The initial products of the reaction between peralkylated triaminophosphanes and bulky alkyl azides, phosphazides 1a-f, were isolated in all cases in good to quantitative yield. The structures of 1d and 1e were confirmed by single-crystal X-ray diffraction. Acidic hydrolysis of pyrrolidino-substituted phosphazide (pyrr)3PN3tBu 1d led to the quantitative formation of aminophosphonium salt (pyrr)3PNH2+· BF4- 8, a direct precursor to a Schwesinger's "building block" synthetic unit. Thermally induced denitrogenation of the phosphazides, which is the second step performed in most cases under solvent-free conditions gave P1 phosphazene bases 2a-f in moderate to excellent yields. A "one-pot" two-step synthesis of phosphazene bases from commercially available triaminophosphanes was discovered. Most of the syntheses were performed on a large laboratory scale. The basicities of the newly synthesized bases 2e and 2f were determined. X-ray crystal structures were obtained for base 2e and for protonated species 2d·HBF4, 2e·HBF4, and 2f·HOTs, which provided the crucial geometrical parameters around the basic center. A rationale for the higher basicity of the pyrrolidino- (pyrr)3P=NR than the piperidino- (pip)3P=NR phosphazenes is presented. A Staudinger reaction was successfully used for the synthesis of a number of sterically congested electron-rich P1 phosphazene bases in moderate to quantitative yield. The intermediate phosphazides were isolated and characterized in all cases; their application in the preparation of higher-order phosphazenes is described. Copyright
Solid-phase chemical synthesis of phosphonoacetate and thiophosphonoacetate oligodeoxynucleotides
Dellinger, Douglas J.,Sheehan, David M.,Christensen, Nanna K.,Lindberg, James G.,Caruthers, Marvin H.
, p. 940 - 950 (2007/10/03)
Phosphonoacetate and thiophosphonoacetate oligodeoxynucleotides were prepared via a solid-phase synthesis strategy. Under Reformatsky reaction conditions, novel esterified acetic acid phosphinodiamidites were synthesized and condensed with appropriately protected 5′-O-(4, 4′-dimethoxytrityl)-2′-deoxynucleosides to yield 3′-O-phosphinoamidite reactive monomers. These synthons when activated with tetrazole were used with an automated DNA synthesizer to prepare phosphonoacetic acid modified internucleotide linkages on controlled pore glass. The phosphinoacetate coupling products were quantitatively oxidized at each step with (1S)-(+)-(10-camphorsulfonyl)oxaziridine or 3H-1,2-benzodithiol-3-one-1,1-dioxide to produce mixed sequence phosphonoacetate and thiophosphonoacetate oligodeoxynucleotides with an average per cycle coupling efficiency of greater than 97%. Completely deprotected, modified oligodeoxynucleotides were purified by reverse-phase HPLC and characterized by ion exchange HPLC, 31P NMR, and MALDI/TOF mass spectroscopy. Both analogues were stable toward hydrolysis with snake venom phosphodiesterase and stimulated RNase H1 activity.
N-pyrrolyl phosphines: An unexploited class of phosphine ligands with exceptional π-acceptor character
Moloy, Kenneth G.,Petersen, Jeffrey L.
, p. 7696 - 7710 (2007/10/02)
The coordination chemistry of N-pyrrolyl phosphines (P-NC4H4) is described. These ligands are prepared in excellent yield from pyrrole, a phosphorus halide, and base, and this synthesis has been applied to the series PPhx(pyrrolyl)3-x (x = 0-2) and the chelate (pyrrolyl)2P(CH2)2P(pyrrolyl)2. These ligands readily form coordination complexes, and the complexes trans-RhCl(CO)[PPhx(pyrrolyl)3-x]2 (x = 0-2) and Mo(CO)4[(pyrrolyl)2P(CH2) 2-P(pyrrolyl)2] are described. The carbonyl stretching frequencies of these complexes are shifted to significantly higher energy relative to "traditional" phosphine ligands, indicating that N-pyrrolyl phosphines are poor σ-donors, exceeding phosphites and approaching fluoroalkylphosphines with respect to this property. For example, νCO for trans-RhCl(CO)-[P(pyrrolyl)3]2 exceeds that of the PPh3 analogue by 59 cm-1. That these ligands are π-acceptors is suggested by the single crystal X-ray structure of trans-RhCl(CO)[P(pyrrolyl)3]2 which shows shortened Rh-P distances and a lengthened Rh-C distance, consistent with enhanced Rh to P back-bonding. The X-ray structure of trans-RhCl(CO)-[P(pyrrolidinyl)3]2 is also reported; this complex possesses longer Rh-P distances which more closely resemble those found for other complexes of this type. The exceptional π-acceptor character of these ligands is convincingly demonstrated by their substitution chemistry with electron rich [PPN][Rh(CO)4]. P(pyrrolyl)3 is found to displace CO in a stepwise manner to give the entire series [PPN][Rh(CO)4-x{P(pyrrolyl)3}xr] (x = 1-4). Similar results are obtained with (pyrrolyl)2P(CH2)2P(pyrrolyl)2, and the anions [PPN][Rh(CO)x{(pyrrolyl)2P(CH2) 2P(pyrrolyl)2}y] (x = 2, y = 1; x = 0, y = 2) are reported. An X-ray structure analysis of [PPN][Rh(CO){P(pyrrolyl)3}3] shows that the Rh-P bonds in this tetrahedral anion are shorter than those found in the Rh(I) complex, consistent with significantly greater π back-bonding in this more electron rich system. The infrared spectra of these anions again show a substantial shift in νCO to higher frequency relative to other phosphine ligands. The structural results further indicate that PPhx(pyrrolyl)3-x (x = 0-2), PPh3, and P(pyrrolidinyl)3 possess nearly identical steric properties (cone angles). The wide range of electronic properties (π-acceptor/σ-donor) exhibited by this isosteric series, together with their ready availability, suggests that they, and N-pyrrolyl phosphines in particular, may find utility in physical inorganic and organometallic chemistry.
