Robert A. Stockland

Luminescent Au(I)/Cu(I) Alkynyl Clusters with an Ethynyl Steroid and Related Aliphatic Ligands: An Octanuclear Au4Cu4 Cluster and Luminescence Polymorphism in Au3Cu2 Clusters

Gold(I) bis(acetylide) complexes [PPN][AuR(2)] (1-3) where PPN = bis(triphenylphosphine)iminium) and R = ethisterone (1); 1-ethynylcyclopentanol (2); 1-ethynylcyclohexanol (3) have been prepared. The reaction of 1 with [Cu(MeCN)(4)][PF(6)] in a 1:1 or 3:2 ratio provides the octanuclear complex [Au(4)Cu(4)(ethisterone)(8)] (4) or pentanuclear complex [PPN][Au(3)Cu(2)(ethisterone)(6)] (5). Complexes 2 and 3 react with [Cu(MeCN)(4)][PF(6)] to form only pentanuclear Au(I)/Cu(I) complexes [PPN][Au(3)Cu(2)(1-ethynylcyclopentanol)(6)] (6) and [PPN][Au(3)Cu(2)(1-ethynylcyclohexanol)(6)] (7). X-ray crystallographic studies of 1-3 reveal nontraditional hydrogen bonding between hydroxyl groups and the acetylide units of adjacent molecules. Complexes 6 and 7 each form polymorphs in which the structures (6 a,b and 7 a,b,c) differ by Au...Au, Au...Cu, and Cu-C distances. The polymorphs exhibit different emission energies with colors ranging from blue to yellow in the solid state. In solution, pentanuclear clusters 5-7 emit with lambda(max) = 570-580 nm and Phi = 0.05-0.19. Complex 4 emits at 496 nm in CH(2)Cl(2) with a quantum yield of 0.65. Complex 5 exists in equilibrium with 1 and 4 in the presence of methanol, ethanol, ethyl acetate, or water. This equilibrium has been probed by X-ray crystallography, NMR spectroscopy, and luminescence experiments. DFT calculations have been performed to analyze the orbitals involved in the electronic transitions of 4, 6, and 7.

Phospha-Michael additions to activated internal alkenes: steric and electronic effects.

The addition of P(O)-H bonds to internal alkenes has been accomplished under solvent-free conditions without the addition of a catalyst or radical initiator. Using a prototypical secondary phosphine oxide, a range of substrates including cinnamates, crotonates, coumarins, sulfones, and chalcones were successfully functionalized. Highly activated acceptors such as isopropylidenemalononitrile and ethyl 2-cyano-3-methyl-2-butenoate underwent the phospha-Michael reaction upon simple trituration of the reagents at room temperature, whereas less activated substrates such as ethyl cinnamate and methyl crotonate required heating (>150 °C) in a microwave reactor to achieve significant consumption of the starting alkenes. For the latter alkenes, a competing reaction involving disproportionation of the ditolylphosphine oxide into ditolylphosphinic acid and ditolylphosphine was observed at the high temperatures needed to promote the addition reaction.

Modern NMR spectroscopy in education

This book will address the strong call for greater utilization of modern NMR in undergraduate education. There has yet been a book to note the numerous chemistry departments integrating NMR across their curricula. Researchers and educators are developing and implementing innovative experiments and pedagogies that are NMR-enabled. The proposed symposium series book will be the first publication to assemble and present these efforts, and will be a comprehensive resource for educators who wish to update their curricula with modern NMR experimentation. Significant progress has been made by educators in recent years to better incorporate modern NMR as an interdisciplinary tool for problem solving into first and second year courses such as general and organic chemistry; this book will report on and review many of these recent advances in first and second year chemistry. Significantly, the proposed book is explicitly designed as a comprehensive resource to educators. The book will help inform the evolution of chemistry curricula to better incorporate NMR as a tool for supporting interdisciplinary, contextual learning.

Synthesis and structures of hydride-bridged palladium A-frame complexes

Abstract A series of hydride-bridged palladium A-frame complexes [Pd2R2(μ-H)(μ-dppm)2]PF6 has been prepared by reaction of [Pd2Cl2(μ-dppm)2] with 2 equiv. of a Grignard reagent, followed by addition of CBr4, NaBH4 and TlPF6. The mixed palladium–platinum species [PdPtR2(μ-H)(μ-dppm)2]PF6 were generated analogously from [PdPtCl2(μ-dppm)2], whereas the unsymmetrical dipalladium derivatives [Pd2(Mes)R(μ-H)(μ-dppm)2]PF6 were produced from the reaction of [Pd(Mes)(dppm)2]X with [Pd2R2(μ-Cl)2(AsPh3)2], followed by treatment with NaBH4. The complexes were characterized by elemental analysis, 1H and 31P NMR spectroscopy. The solid-state structures of [Pd2(C6H4Me-4)2(μ-H)(μ-dppm)2]BH3CN (1a) (obtained as its BH3CN− salt when NaBH3CN was used instead of NaBH4), [PdPt(C6H4Me-4)2(μ-H)(μ-dppm)2]PF6 (2a), [Pd2(Mes)Et(μ-H)(μ-dppm)2]PF6 (3b), [Pd2(Mes)Ph(μ-H)(μ-dppm)2]PF6 (3c) and [EtPt(μ-H)(μ-dppm)2PdMe]PF6 (4) have been determined by X-ray crystallography. 3c adopts an elongated boat conformation in the solid state, whereas the others exist in the chair form. The unsymmetrical cations 2a and 4 containing smaller organic substituents are disordered in the solid state, whereas the mesityl-containing derivatives 3b and 3c are not.

Demethylation of trimethylphosphite promoted by dichlorodiphosphineplatinum and palladium complexes. Structures of the metallophosphonate complexes [Pt(P∧P){P(O)(OMe)2}2] (P∧P=dppe, dppp)

Abstract Platinum and palladium complexes of the type [MCl2(P∧P)] (P∧P=dppm, dppe, dppp) react with P(OMe)3 at low temperatures to generate the bis(phosphite) species [M(P∧P){P(OMe)3}2]2+, which have been characterized by 31P NMR spectroscopy at low temperatures. On warming, the [M(P∧P){P(OMe)3}2]Cl2 complexes undergo an Arbuzov-like reaction to generate the bis(phosphonate) derivatives [M(P∧P){P(O)(OMe)2}2], which have been characterized by elemental analysis and NMR spectroscopy. The platinum complexes with P∧P=dppe and dppp have been characterized in the solid state by single crystal X-ray diffraction; each complex exhibits square planar geometry about the metal center. [Pt(dppe){P(OMe)3}2][PF6]2 was isolated by performing the reaction of [PtCl2(dppe)] with P(OMe)3 in the presence of 2 mol equiv. of TlPF6, whereas the mixed phosphite–phosphonate complex [Pt(dppe){P(OMe)3}{P(O)(OMe)2}]PF6 was prepared by carrying out the reaction in the presence of only 1 mol equiv. of TlPF6. Formation of the phosphite complexes is rapid and quantitative for both metals, as observed by low temperature 31P NMR spectroscopy. At ambient temperature, an equilibrium exists between free and coordinated phosphite, the latter being favored for platinum but apparently not for palladium. This results in formation of the phosphonate complexes being much faster for Pt than for Pd, unless a considerable excess of P(OMe)3 is added. The demethylation reactions could be reversed by treating [Pt(dppe){P(O)(OMe)2}2] or [Pt(dppe){P(OMe)3}{P(O)(OMe)2}]PF6 with Me3O+BF4−, although the reactions were not quantitative. Protonation of [Pt(dppe){P(O)(OMe)2}2][PF6]2 with HBF4 gave first [Pt(dppe){P(O)(OMe)2}2H]+ and, finally, [Pt(dppe){P(OH)(OMe)2}2]2+.

Transition metal complexes containing P(C6H5)(C6H4Cl-2)2. The effect of added Lewis bases as a probe for substitution reactions occurring in ambient temperature Suzuki couplings catalyzed by Pd/P(C6H5)(C6H4Cl-2)2

The reactivity of the d 8 transition metal complexes, [NiBr 2 (CH 3 OCH 2 CH 2 OCH 3 )] and MCl 2 L 2 (M=Pd, Pt; L=CH 3 CN; L 2 =1,5-cyclooctadiene), towards P(C 6 H 5 )(C 6 H 4 Cl-2) 2 ( 1 ) was investigated. While treatment of [PdCl 2 (cod)] with 2 equiv of 1 resulted in displacement of the weakly coordinating cyclooctadiene and formation of [PdCl 2 (P(C 6 H 5 )(C 6 H 4 Cl-2) 2 ) 2 ], analogous reactions with [PtCl 2 (cod)] afforded the monosubstituted species [PtCl 2 (cod)(P(C 6 H 5 )(C 6 H 4 Cl-2) 2 )]. The disubstituted complex [PtCl 2 (P(C 6 H 5 )(C 6 H 4 Cl-2) 2 ) 2 ] was successfully obtained by treatment of [PtCl 2 (NCCH 3 ) 2 ] with 2 equiv of 1 . However, attempts to react 1 with [NiBr 2 (CH 3 OCH 2 CH 2 OCH 3 )] were unsuccessful. The chlorinated triphenyl phosphine is quite labile and is readily displaced from [PdCl 2 (P(C 6 H 5 )(C 6 H 4 Cl-2) 2 ) 2 ] by various Lewis bases including nitrogen containing ligands such as 2,2′-bipyridine. The molecular structure of trans -[PdCl 2 (P(C 6 H 5 )(C 6 H 4 Cl-2) 2 ) 2 ] was determined by X-ray diffraction and represents the first molecular structure determination of a transition metal complex containing 1 . This complex crystallizes in the monoclinic space group P 2 1 / n with a =10.3928(3) A, b =16.0102(4) A, c =13.1884(4) A, β =90.714(2)°, and Z =4. Key geometric parameters include PdCl(1) = 2.309(1) A, PdP(1)=2.334(1) A; PdP(1)C(7)=118.3(2)°, PdP(1)C(1)=115.3(2)°, C(1)C(6)Cl(2)=120.7(4)° and Cl(1)PdP(1)=85.86(4)°.

Resolved P-Metalated Nucleoside Phosphoramidites

The synthesis of resolved P-metalated nucleoside phosphoramidites is described. These rare compounds were initially prepared with gold as the metal center; however, the gold can be removed using basic phosphines or solid-supported triphenylphosphine. Treatment of the free nucleoside phosphoramidite with a platinum source generated a unique platinated dinucleoside species with a diastereomeric ratio of >99:1.

Synthesis of Spirocyclic Diphosphite-Supported Gold Metallomacrocycles via a Protodeauration/Cyclization Strategy: Mechanistic and Binding Studies

A spirocylic diphosphite was used to generate P-metalated bimetallic complexes through protodeauration reactions involving LAuC6H4tBu (L = JohnPhos, tBuXPhos) and metallomacrocycles through protodeauration/cyclization using tBuC6H4AuP^PAuC6H4tBu precursors (P^P = flexible diphosphine). While the synthesis of the bimetallic complexes followed a stepwise process, generation of the metallomacrocycles was highly complex because of a series of reversible ligand redistribution reactions. The self-assembly was monitored, and key intermediates were identified by NMR spectroscopy and high-resolution mass spectrometry. The mechanistic investigation showed that using flexible diphosphine linkers was critical to the selective synthesis of metallomacrocycles because rigid diphosphines generated intractable mixtures of linear and cyclic compounds. The X-ray structure of a 32-membered metallomacrocycle revealed that the compound crystallized in an unsymmetrical collapsed form that was held together by two supported aurophilic interactions while the flexible diphosphines were folded along opposite sides of the metallomacrocycle. The solution structure was consistent with a symmetric species, which suggested interconversion between an open and collapsed form and/or rapid twisting of a collapsed form. The 32-membered metallomacrocycle was used to bind estrogen primarily through the formation of AuP-O-···H-OR hydrogen bonds.