Synthesis and characterization of cationic dicarbonyl Fe(II) PNP pincer complexes.

ABSTRACT: In the present work, we have prepared a series of octahedral Fe(II) complexes of the type trans-[Fe(PNP)(CO)2Cl]+-PNP are tridentate pincer-type ligands based on 2,6-diaminopyridine. These complexes are formed irrespective of the size of the substituents at the phosphorus sites and whether cis-[Fe(PNP)(Cl2)(CO)] or trans-[Fe(PNP)(Cl2)(CO)] are reacted with CO in the presence of 1 equiv of silver salts. X-ray structures of representative complexes are presented. Based on simple bonding considerations the selective formation of trans-dicarbonyl Fe(II) complexes is unexpected. In fact, DFT calculations confirm that trans-dicarbonyl complexes are indeed thermodynamically disfavored over the respective cis-dicarbonyl compounds, but are favored for kinetic reasons.

Twinning of three Fe-PNP pincer complexes interpreted according to order-disorder (OD) theory.

The systematic twinning of three 2,6-diaminopyridine-based Fe-PNP complexes is interpreted using order-disorder (OD) theory. The monoclinic [Fe(0)(PNP(Et)-(i)Pr)(CO)2] [P112(1)/b, Z' = 4] possesses pseudo-orthorhombic metrics and crystallizes as a reflection twin by pseudo-merohedry with the twin plane (100). The structure is made up of layers with idealized p2(1)a(b) symmetry. The a glide planes of adjacent layers do not overlap, leading to OD polytypism. trans-[Fe(II)(PNP-Et)Br2(CO)] [P2(1)/n, Z' = 1] is systematically twinned via twofold rotation about [001]. It is made up of OD layers with idealized p2(1)2(1)(2) symmetry. OD polytypism is caused by the twofold rotation axes of adjacent layers which do not overlap. [Fe(II)(κ(2)P,N-PNP-(i)Pr,TAD)Cl2]·THF [P1, Z^{\prime} = 2] is systematically twinned via a twofold rotation about [010]. It is made up of layers with idealized p121(1) symmetry. OD polytypism is caused by screw rotations relating adjacent layers with an intrinsic translation along a fourth of a primitive lattice vector. In all three structures the twin individuals are a polytype with a maximum degree of order (MDO) and at the twin interface is located a fragment of the second MDO polytype.

Iron(II) complexes featuring κ3- and κ2-bound PNP pincer ligands--the significance of sterics.

Treatment of anhydrous FeX2 (X = Cl, Br) with 2 equiv. of the sterically little demanding N,N'-bisphosphino-2,6-diaminopyridine based PNP ligands--featuring Ph, biphenol (BIPOL), Me, Et, nPr, and nBu substituents at the phosphorus sites and H, Me, and Ph substituents at the N-linkers--afforded diamagnetic cationic octahedral complexes of the general formula [Fe(κ(3)-P,N,P-PNP)(κ(2)-P,N-PNP)X](+) featuring a κ(2)-P,N bound PNP ligand. With the sterically more encumbered N-methylated ligand PNP(Me)-Ph the related complex [Fe(κ(3)-P,N,P-PNP(Me)-Ph)(κ(2)-P,N-PN(HMe)-Ph)Cl](+) rather than [Fe(κ(3)-P,N,P-PNP(Me)-Ph)Cl2] was formed. This reaction was accompanied by P-N bond cleavage, thereby forming the κ(2)-P,N-bound N-diphenylphosphino-N,N'-methyl-2,6-diaminopyridine ligand. In contrast, with the N-phenylated ligands PNP(Ph)-Et and PNP(Ph)-nPr, despite small Et and nPr substituents at the phosphorus sites, complexes [Fe(κ(3)-P,N,P-PNP(Ph)-Et)Cl2] and [Fe(κ(3)-P,N,P-PNP(Ph)-nPr)Cl2] were formed, revealing that sterics can be also controlled by substituent variations at the amino N-sites. Depending on the solvent, complexes featuring κ(2)-P,N-bound ligands undergo facile rearrangement reactions to give dicationic complexes of the type [Fe(κ(3)-P,N,P-PNP)2](2+) where both PNP ligands are bound in a κ(3)-P,N,P-fashion. In the presence of either Ag(+) or Na(+) salts as halide scavengers this reaction takes place within a few minutes. The pendant PR2 arm of the κ(3)-κ(2)-complexes is readily oxidized to the corresponding phosphine sulfides upon treatment with elemental sulfur. This was exemplarily shown for [Fe(κ(3)-P,N,P-PNP-nPr)(κ(2)-P,N-PNS-nPr)Cl](+). Halide abstraction afforded the dicationic bis-chelated octahedral Fe(II) complex [Fe(κ(3)-P,N,P-PNP)2](2+) together with the free SNP ligand rather than [Fe(κ(3)-P,N,P-PNP-nPr)(κ(3)-S,P,N-PNS-nPr)](2+).

Secondary confounders of osteoporotic hip fractures in patients admitted to a geriatric acute care department.

BACKGROUND: With respect to the pathogenesis of osteoporosis, primary and secondary forms of the disease can be distinguished. It has been recognized that the incidence of primary and secondary osteoporosis differs in women and men. OBJECTIVE: The aim of the present study was to assess the incidence and gender distribution of factors contributing to osteoporosis in older hip fracture patients. METHODS: In this cross-sectional study 404 patients with hip fractures and controls referred to an acute geriatric care department over a period of 15 months were included. The medical history was recorded and blood samples were analyzed for routine laboratory parameters. RESULTS: A total of 249 patients with hip fractures and 155 matched controls were studied. The Tinetti test and the Barthel index were found to show highly significant differences in both groups mainly because of the postoperative state of patients with fractures. Vitamin D deficiency was found in 94.1% of male fracture patients and 94.6% of female fracture patients. On average 2.4 secondary contributors of osteoporosis were present in male fracture patients versus 2.9 in male controls and 2.3 in female fracture patients versus 2.3 in female controls. For most parameters no significant gender differences of possible secondary contributors to osteoporosis were found. Secondary osteoporosis was diagnosed in all male fracture patients and in 56.2% of all female fracture patients. CONCLUSION: Based on the findings of this study it is recommended that hip fracture patients should be assessed for secondary contributors of osteoporosis. Although the overall distribution of secondary contributors was similar in women and men, the prevalence of secondary osteoporosis was higher in men.

Crystal structure of N,N'-bis-(diiso-propyl-phosphan-yl)-4-methyl-pyridine-2,6-di-amine.

In the mol-ecule of the title compound, C18H35N3P2, the methyl-pyridine-2,6-di-amine moiety is almost planar, with a maximum deviation of 0.0129 (9) Šfor one of the amine N atoms. Whereas one of the P atoms is co-planar with this mean plane [deviation = 0.0158 (10) Å], the other P atom is considerably displaced out of the mean plane by 0.5882 (10) Å. In the crystal, no directional intermolecular interactions beyond van der Waals contacts could be identified.

An iron(II) complex featuring κ(3) and labile κ(2)-bound PNP pincer ligands - striking differences between CH2 and NH spacers.

Treatment of anhydrous FeCl2 with 2 equiv. of the pincer ligand PNP-Ph afforded the diamagnetic cationic octahedral complex [Fe(κ(3)-P,N,P-PNP)(κ(2)-P,N-PNP)Cl](+) featuring a κ(2)-P,N-bound PNP ligand. Preliminary reactivity studies revealed that the κ(2)-P,N-bound PNP ligand is labile reacting with CO to afford trans-[Fe(PNP-Ph)(CO)2Cl](+).

Heterolytic Cleavage of Dihydrogen by an Iron(II) PNP Pincer Complex via Metal-Ligand Cooperation.

The bis-carbonyl Fe(II) complex trans-[Fe(PNP-iPr)(CO)2Cl]+ reacts with Zn as reducing agent under a dihydrogen atmosphere to give the Fe(II) hydride complex cis-[Fe(PNP-iPr)(CO)2H]+ in 97% isolated yield. A crucial step in this reaction seems to be the reduction of the acidic NH protons of the PNP-iPr ligand to afford H2 and the coordinatively unsaturated intermediate [Fe(PNPH-iPr)(CO)2]+ bearing a dearomatized pyridine moiety. This species is able to bind and heterolytically cleave H2 to give cis-[Fe(PNP-iPr)(CO)2H]+. The mechanism of this reaction has been studied by DFT calculations. The proposed mechanism was supported by deuterium labeling experiments using D2 and the N-deuterated isotopologue of trans-[Fe(PNP-iPr)(CO)2Cl]+. While in the first case deuterium was partially incorporated into both N and Fe sites, in the latter case no reaction took place. In addition, the N-methylated complex trans-[Fe(PNPMe-iPr)(CO)2Cl]+ was prepared, showing no reactions with Zn and H2 under the same reaction conditions. An alternative synthesis of cis-[Fe(PNP-iPr)(CO)2H]+ was developed utilizing the Fe(0) complex [Fe(PNP-iPr)(CO)2]. This compound is obtained in high yield by treatment of either trans-[Fe(PNP-iPr)(CO)2Cl]+ or [Fe(PNP-iPr)Cl2] with an excess of NaHg or a stoichiometric amount of KC8 in the presence of carbon monoxide. Protonation of [Fe(PNP-iPr)(CO)2] with HBF4 gave the hydride complex cis-[Fe(PNP-iPr)(CO)2H]+. X-ray structures of both cis-[Fe(PNP-iPr)(CO)2H]+ and [Fe(PNP-iPr)(CO)2] are presented.