R. K. Bansal

Synthesis and characterization of diorganotin(IV) complexes of tetradentate Schiff bases: Crystal structure of n-Bu2Sn(Vanophen)

Abstract Diorganotin(IV) complexes of the general formula R2SnL (R=Ph, n-Bu and Me) have been prepared from diorganotin(IV) dichlorides (R2SnCl2) and tetradentate Schiff bases (H2L) containing N2O2 donor atoms in the presence of triethylamine in benzene. The Schiff bases, H2L, were derived from salicylaldehyde, 3-methoxysalicylaldehyde (o-vanillin), 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone and diamines such as o-phenylenediamine and 1,3-propylenediamine. The complexes were characterized by IR, NMR (1H, 13C, 119Sn) and elemental analysis. The structure of the complex, n-Bu2Sn(Vanophen), was determined using single crystal X-ray diffraction. The tin atom has a distorted octahedral coordination, with the Vanophen ligand occupying the four equatorial positions and the n-butyl groups in the trans axial positions. Six-coordinated distorted octahedral structures have been proposed for all diorganotin(IV) complexes studied here, as they possess similar spectroscopic data.

Synthesis of 1H-1,3-benzazaphospholes: substituent influence and mechanistical aspects

Abstract Various substituted carboxylic acid 2-chloro- and 2-bromoanilides 1a–j react with triethylphosphite in the presence of anhydrous NiCl2 or NiBr2 to give o-acylamido-benzenephosphonic acid esters 2a–g and 2j. Yields depend strongly on the substituents. 2-Fluoro-4,6-dibromoacetanilide 1g reacts only at 6-position, indicating an o-directed process. Based on substituent effects, we infer a mechanism via Ni(0) intermediates that insert into the carbon–halogen bond. The N-tertiary 2-bromoformanilide 4 does not undergo phosphonylation to 5 in the presence of the Ni-catalyst but reacts in the presence of Pd-catalysts. The subsequent reduction of the N-secondary o-acylamido-benzenephosphonic acid esters 2 with excess LiAlH4 is coupled with an intramolecular cyclisation to the 1H-1,3-benzazaphospholes 6 whereas the N-tertiary derivative 5 does not undergo cyclisation upon reduction. NMR data and the crystal structure of 6d are reported.

Metalated 1, 3-Azaphospholes: η1-(1H-1, 3-Benzazaphosphole-P)M(CO)5 and μ2-[(1, 3-Benzazaphospholide-P)(cyclopentadienide)nickel] Complexes†

1H-1, 3-Benzazaphospholes react with M(CO)5(THF) (M = Cr, Mo, W) to give thermally and relatively air stable η1-(1H-1, 3-Benzazaphosphole-P)M(CO)5 complexes. The 1H- and 13C-NMR-data are in accordance with the preservation of the phosphaaromatic π-system of the ligand. The strong upfield 31P coordination shift, particularly of the Mo and W complexes, forms a contrast to the downfield-shifts of phosphine-M(CO)5 complexes and classifies benzazaphospholes as weak donor but efficient acceptor ligands. Nickelocene reacts as organometallic species with metalation of the NH-function. The resulting ambident 1, 3-benzazaphospholide anions prefer a μ2-coordination of the η5-CpNi-fragment at phosphorus to coordination at nitrogen or a η3-heteroallyl-η5-CpNi-semisandwich structure. This is shown by characteristic NMR data and the crystal structure analysis of a η5-CpNi-benzazaphospholide. The latter is a P-bridging dimer with a planar Ni2P2 ring and trans-configuration of the two planar heterocyclic phosphido ligands arranged perpendicular to the four-membered ring. Metallierte 1, 3-Azaphosphole: η1-(1H-1, 3-Benzazaphosphol-P)M(CO)5 und μ2-[(1, 3-Benzazaphospholid-P)(cyclopentadienid)nickel] Komplexe 1H-1, 3-Benzazaphosphole reagieren mit M(CO)5(THF) (M = Cr, Mo, W) zu thermisch und zumindest kurzzeitig luftstabilen η1-(1H-1, 3-Benzazaphosphol-P)M(CO)5-Komplexen. Die 1H- und 13C-NMR-Daten sind mit dem Erhalt des phosphaaromatischen π-Systems im Liganden im Einklang. Die starke 31P-Koordinationsverschiebung zu hohem Feld, vor allem der Mo- und W-Komplexe, steht im Gegensatz zur Koordinationsverschiebung zu tiefem Feld, beobachtet bei Phosphin-M(CO)5 Komplexen, und verweist auf schwache Donator-, aber gute Akzeptoreigenschaften der Liganden. Nickelocen reagiert als Ubergangsmetallorganyl unter Metallierung der NH-Funktion. Die resultierenden ambidenten 1, 3-Benzazaphospholid-Anionen bevorzugen eine μ2-Koordination des η5-CpNi-Fragments am Phosphor gegenuber N-Koordination oder einer η3-Heteroallyl-η5-CpNi-Semisandwich-Struktur. Dies wird durch charakteristische NMR-Daten und die Ergebnisse der Strukturuntersuchung an Einkristallen eines η5-CpNi-benzazaphospholids belegt. Letzteres kristallisiert mit Benzol und bildet ein P-Bruckendimer mit planarem Ni2P2 Ring und trans-Konfiguration der beiden senkrecht zum Vierring angeordneten planaren heterocyclischen Phosphidoliganden.

Derivative spectrophotometric determination of iridium after preconcentration of its 1-(2-pyridylazo)-2-naphthol complex on microcrystalline naphthalene

Iridium is preconcentrated from the large volume of its aqueous solution using 1-(2-pyridylazo-2-naphthol) (PAN) on microcrystalline naphthalene in the pH range of 4.5-6.0. The solid mass after filtration is dissolved with 5 ml of dimethylformamide (DMF) and the metal determined by first derivative spectrophotometry. The detection limit is 20 ppb (signal to noise ratio = 2) and the calibration curve is linear over the concentration range 0.25-75.0 mug in 5 ml of the final DMF solution with a correlation coefficient of 0.9996 and relative standard deviation of +/- 1.1%. Various parameters such as the effect of pH, volume of aqueous phase, choice of solvent, reagent and naphthalene concentration, shaking time and interference of a number of metal ions on the determination of trace amount of iridium have been studied in detail to optimize the conditions for its determination in synthetic samples corresponding to various standard alloys and environmental samples.

Metalated 1,3-azaphospholes: synthesis of lithium-1,3-benzazaphospholides and reactivity towards organoelement and organometal halides

Abstract Metalation of benzazaphospholes 1a – e with t -BuLi provided the ambident anions 1a – e Li in high selectivity. A crystal structure analysis of 1b Li ·3THF reveals monomers and coordination of lithium at nitrogen. The tungsten pentacarbonyl complexes also react preferably at nitrogen as shown by the reaction of 2a and 2d with t -BuLi. Addition at the PC bond is a minor process in the case of 2a . Compounds 1a , c Li as well as 2d Li react with alkyl halides at phosphorus to give the 3-alkyl-1,3-benzazaphospholes 3a and 3d or the respective W(CO) 5 complex 4d . Even acetyl and pivaloyl chloride attack 1e Li at phosphorus affording the P -acyl derivatives 5e and 6e . Silylation can occur at nitrogen or phosphorus to give 7 and/or 8 depending on steric and electronic effects exerted by the substituent in position 2. The different effect of 2- t -butyl groups on the steric hindrance at N and P is illustrated by the molecular geometry of 1d determined by crystal structure analysis. Soft organometallic halides such as Me 3 SnCl, CpFe(CO) 2 I and CpW(CO) 3 Cl react with 1 Li preferably at phosphorus affording the stannyl or monomer organo-transition metal derivatives 9 – 11 . The products are characterized by multinuclear NMR data of all new compounds.

2-Phosphaindolizines via 1,5-electrocyclization

Abstract N-Pyridinium dichlorophosphinomethylides disproportionate to generate bis(N-pyridinium ylidyl)phosphenium chloride which undergoes 1,5-electrocyclization to give 2-phosphaindolizines. In one-pot synthesis N-(alkoxycarbonylmethyl)pyridinium bromide reacts with PCl 3 in presence of Et 3 N to form 2-phosphaindolizine.

Complexes of Azaphospholes: Synthesis and Structure of Pentacarbonyl-(η1)-2-phosphaindolizine)chromium(0), -molybdenum(0), and -tungsten(0)

The complex chemical behaviour of 2-phosphaindolizines 1 (1,3-azaphospholo[1,5-a]pyridines) towards metal carbonyl compounds was studied. (η1-2-Phosphaindolizine)M(CO)5 complexes 2–4 (M = Cr, Mo, W) were formed from 1 and [(THF)M(CO)5], the cis-L2Cr(CO)4 complex 5f from 1f and tetracarbonyl(norbornadiene) chromium(0). The reaction of 2-phosphaindolizines 1e, 1f, or 1g with tricarbonyl(cycloheptatriene)molybdenum(0) or tricarbonyl(mesitylene)tungsten(0) yielded σ-complexes of the types L2M(CO)4or L3M(CO)3 rather than isolable π-complexes. In one case a strong upfield signal (δ31P = 6.1) was observed with a coordination shift of Δδ = –161.7, which is typical for π-coordination. Prolonged reaction or work-up led, however, to dismutation yielding 1g and the fac-L3Mo(CO)3 complex 6g. X-ray structure analysis of 2a indicates an increased 10π-delocalization compared with 1a and a changed conformation of the acyl substituent. The influence of substituents and metals on the 31P and 13C complexation chemical shifts and coupling constants is discussed.

Stereo- and regioselectivity in Diels-Alder reactions of 1,3-azaphospholo[5,1-a]isoquinoline and -[1,5-a]pyridine

Abstract 1,3-Bis(ethoxycarbonyl)-1,3-azaphospholo[5,1-a]isoquinoline and -[1,5-a]pyridine undergo stereoselective Diels–Alder reactions at the CP– functionality with 2,3-dimethylbutadiene and isoprene in the presence of sulfur or methyl iodide. The reaction with isoprene occurs regioselectively as well, as confirmed by an X-ray crystal structure determination of one cycloadduct. Semiempirical PM3 calculations also support the regioselectivity.

Metalated 1,3‐Azaphospholes: 1H‐1,3‐Benzazaphosphole and 1,3‐Benzazaphospholide Tungsten(0) and Tungsten(II) Complexes

2-tert-Butyl-1H-1,3-benzazaphosphole (1a) reacts with tBuLi without addition to the P=C bond to form a lithium benzazaphospholide that affords the η1-(benzazaphospholide-P)tungsten(II) complex 2 upon reaction with [CpW(CO)3Cl]. It is sensitive to alcoholysis and to air oxidation yielding 1a and the P-oxo-benzazaphospholide complex 3, respectively. The (1,3-benzazaphosphole)pentacarbonyltungsten complex 4, obtained from 1b and [W(CO)5(THF)], reacts preferentially with tBuLi by lithiation of the NH function and is attacked by [CpW(CO)3Cl] at phosphorus to give the mixed valence bimetallic tungsten(II)-tungsten(0) benzazaphospholide complex 5. A side product, (3-tert-butyl-2-methyl-1,3-benzazaphosphole)pentacarbonyltungsten (6), is attributed to side-reaction where tBuLi adds to the P=C bond in 4. The composition of the products was determined from X-ray structure analysis of 3 and spectroscopic data.

Studies on some di- and triorganotin(IV) derivatives of bis(1-pyrazolyl) borates and some related compounds

Abstract A number of di- and triorganotin(IV) complexes of dihydrobis(1-pyrazolyl)borate and diphenylbis(1-pyrazolyl)borate have been synthesized. The complexes derived from dihydrobis(1-pyrazolyl)borate have been converted to their dihalobis(1-pyrazolyl)borate analogues by halogenation reactions. The compounds have been characterized by elemental analysis, infrared and 1 H, 11 B and 119 Sn NMR spectra.