Michael Lattman

Calixarenes as a new class of external electron donors in Ziegler-Natta polypropylene catalysts

Abstract In this work we have shown that calixarenes form a new type of external donor ligand which can function effectively as a selectivity control agent to increase the yield of isotactic polypropylene in late-generation Ziegler–Natta catalysts. The procatalyst prepared utilized dibutylphthalate as the internal donor to function with the calixarene. We have synthesized and characterized a wide variety of new substituted calixarenes containing hydroxy- and methoxy-end groups. All of these calixarenes were evaluated in the bulk polymerization of propylene and found to increase significantly the amount of i-PP formed relative to reactor runs performed without the calixarene.

Ultraviolet photoelectron spectra of 4-substituted pyridine-pentacarbonylchromium complexes

Abstract The ultraviolet photoelectron spectra of Cr(CO) 5 (4-RPyr) have been measured, and the IPs observed below 12 eV are discussed. Bands found in the region 7-8 eV are assigned to ionization from the chromium d orbitals. The IP values are shown to increase with the increasing electron acceptor nature of the ring substituents. The remaining bands below 12 eV are assigned to the pyridine orbitals. The IP values of the uncomplexed pyridines are observed to increase upon complexation, and a comparison is made of the effects of complexation with the Cr(CO) 5 and BH 3 moieties.

Reactivity of transition metal-substituted phosphoranes: crystal and molecular structure of 2-pentacarbonylmanganese-1,3,2-benzodioxaphosphole-2-oxide

The crystal and molecular structure of 2-pentacarbonylmanganese-1,3,2-benzodi-oxaphosphole-2-oxide,OC6H4OP(O)Mn(CO)5, has been determined by single crystal X-ray diffraction. The crystal belongs to the triclinic system with a space group of P1. The unit cell parameters are: a 6.753(2), b 8.818(3), c 12.004(4) A, α 106.79(2), β 105.37(2), γ 98.82(2)°, and Z = 2. Graphite monochromatic Mo-Kα radiation was used in the intensity measurements. The final disagreement index was 0.073 for 2293 reflections. The Mn and P atoms have distorted octahedral and tetrahedral configurations, respectively. The phenyl ring is essentially planar; however, the dioxaphosphole 5-membered ring is slightly puckered. The PO has an almost eclipsed conformation with one of the equatorial carbonyls, leading to pseudo mirror symmetry.

Main-Group Chemistry within Macrocyclic Rings and Baskets

Abstract The incorporation of main-group elements into macrocycles leads to stabilization of novel structures and control of reactivity. The tetraamino macrocycle cyclen appears to favor a pentacoordinate trigonal bipyramidal (tbp) geometry about phosphorus, even when phosphorus is bonded to transition-metals. The tbp geometry is also favored for arsenic. The tetraphenol macrocycle p-tert-butylcalix[4]arene appears to stabilize a hexacoordinate phosphorus geometry under certain conditions; however, pentacoordinate and tricoordinate structures are also found.

Metallophosphoranes: Carbonyl substitution reactions and the X-ray crystal structure of cis-Cat2PMn(CO)4P(OPh)3 (Cat = benzodioxyl)

Abstract Cat 2 PMn(CO) 5 (1, cat = ) is found to undergo carbonyl substitution reactions with phosphorus donors to give the isolable products cat 2 PMn(CO) 4 L, where L = cis -PPh 3 ( 2 ); trans -PPh 3 ( 3 ); cis -P(OMe) 3 ( 4 ); and cis -P(OPh) 3 ( 5 ). No evidence for CO insertion into the pentacoordinate PMn bond is observed. The X-ray crystal structure of 5 shows that the crystals are monoclinic, space group P 2 1 / n . The unit cell parameters are: a 10.523(2), b 25.765(5), c 13.344(2) A, β 99.11(2)°, and Z = 4. Full matrix least squares refinement reached R = 0.054 for 3099 observed reflections. The pentacoordinate phosphorus adopts a distorted trigonal bipyramid geometry with the Mn in an equatorial position. Noteworthy is the small equatorial OPO angle of 110.1(2)°.

Synthesis and Reactivity of Transition Metal-Substituted Phosphoranes

Abstract The synthesis of 1, by nucleophilic substitution of Cl− by Mn(CO)5 − is described. The hydrolysis reactions of 1 lead to two compounds containing P-Mn bonds whose structures have been determined by x-ray crystallography.

Phosphorus-Based Calix[4]arene Ligands Bound to Metals through Oxygen

Calixarenes containing phosphorus are useful ligands toward transition metals. We report complexes of calix[4]arenes in which metal binding is through one of the oxygens of the calixarene backbone.

Variable Coordination of Phosphorus within Calixarenes and Complexing Abilities of Phosphorus-Based Calixarenes

Solvent-dependent coordination of phosphorus within a calix[4]arene cavity is shown and the differences in the abilities of a ligand to bind to a metal within calix[4]arenes and calix[5]arenes is demonstrated.

Direct transformation of six- to three-coordinate phosphorus in p-tert-butylcalix[4]arene; the first X-ray crystal structure of a hypervalent main group atom bound to a calixarene

Removal of dimethylamine from the zwitterionic six-coordinate phosphorus species p-fert-butylcalix[4]areneP(H)NHMe21 leads to the three-coordinate derivative p-tert- butylcalix[4]arene(H)P 4; the X-ray structure of Li[p-tert-butylcalix[4]areneP(H)NMe2]3 gives an insight as to why no pentacoordinate species is observed.

Reactions of a Cyclenphosphoranide Platinum (II) Complex and the Role of Highly Nucleophilic Substituents at the Axial Positions of a Trigonal Bipyramid

Abstract (η2-cyclenP)Pt(Cl)PPh3 1 exhibits a large variety of selective reactions due to the platinum metal and cyclenphosphoranide ligand, cyclenP. Moreover, the cyclenP ligand is capable of altering many of the usual reactions and/or mechanisms at square planar platinum (II) complexes.