Palladium-catalysed reactions of aryl halides with soft, non-organometallic nucleophiles

Dynamic kinetic resolution

Multifunctional ligands with podand topology provide intrinsically well-defined coordination geometries. Several subgroups of multidentate ligand systems comprising dual functionality have been developed so far. Recent advances made in this research area reflect its topicality. Work on metal complexes of ambiphilic ligands consisting of Lewis-acidic Group 13 element bridgehead atoms and additional donor functionalities is in the current focus of interest. The intrinsic topology of tetradentate ligands may introduce a fascinating reactivity and interesting electronic properties to the metal complexes. Janus-head type ligands are very promising candidates for the preparation of multimetallic complexes.

Multidentate ligand systems featuring dual functionality

The cation−π interaction is an attractive noncovalent interaction between a cation and a π system. Due to the stronger interaction energy than those of the other π interactions, such as π–π and CH−π interactions, the cation−π interaction has recently been recognized as a new tool for controlling the regio- and stereoselectivities in various types of organic reactions. This review attempts to cover a variety of organic reactions controlled by cation−π interactions, which includes not only recent examples but also those reported before the term “cation−π interaction” was defined in 1990. This review will provide comprehensive knowledge on the role of cation−π interactions in organic synthesis.

Cation-π Interactions in Organic Synthesis.

This paper provides a short introduction to the basics of electron density investigations. The two predominant approaches for the modelling and various interpretations of electron density distributions are presented. Their potential translations into chemical concepts are explained. The focus of the article lies on the deduction of chemical properties from charge density studies in some selected main group compounds. The relationship between the obtained numerical data and commonly accepted simple chemical concepts unfortunately is not always straightforward, and often the chemist relies on heuristic connections rather than rigorously defined ones. This article tries to demonstrate how charge density analyses can shed light on aspects of chemical bonding and reactivity resulting from the determined bonding situation. Sometimes this helps to identify misconceptions and sets the scene for new unconventional synthetic approaches.

Meaningful Structural Descriptors from Charge Density

Phosphane- and phosphorane Janus Head ligands in metal coordination

Trimethylsilyliminotriphenylphosphoran Ph3P=NSiMe3 (1) reagiert mit metallischem Natrium in THF unter Spaltung einer P–CPhenyl-Bindung zu Natriumdiphenylphosphanyltrimethylsilylamid [(THF)3Na(Ph2PNSiMe3)] (2). Anschliesende Reaktion mit Ammoniumbromid oder Hydrolyse mit Wasser ergibt Diphenylphosphanyltrimethylsilylamin Ph2PN(H)SiMe3 (3) und bei der Hydrolyse mit Wasser in geringen Mengen das oxidierte Nebenprodukt [(THF)Na(OOPPh2)]n (4), das gezielt durch die Reaktion von Ph2POOH mit NaH in THF erhalten werden kann. Ph2PN(H)SiMe3 (3) reagiert mit einem Aquivalent Zn{N(SiMe3)2}2 zu [(Me3Si)2NZnPh2PNSiMe3]2 (5). Mit Caesium reagiert 3 unter Phosphor-Phosphor-Bindungsknupfung in einer reduktiven Substituentenkopplungsreaktion zu [(THF)Cs2{Ph(NSiMe3)P}2]n (6). Phosphor(III) wird dabei zu Phosphor(II) reduziert. Phosphor-Phosphor-Bindungsknupfung unter Oxidation der Phosphoratome von PIII zu PIV erfolgt bei der Darstellung von (Ph2PNSiMe3)2 (7) durch Lithiierung von 3 und anschliesender Umsetzung mit Bismuttrichlorid.



Synthesis and Reactivity of the Diphenylphosphanyltrimethylsilylamine Ph2PN(H)SiMe3



The trimethylsilyliminotriphenylphosphoran Ph3P=NSiMe3 (1) reacts with sodium in THF under cleavage of one P–Cphenyl bond leading to the PIII-species [(THF)3Na(Ph2PNSiMe3)] (2). Reaction with NH4Br or hydrolysis with water gives the diphenylphosphanyltrimethylsilylamine Ph2PN(H)SiMe3 (3) and in low yields the oxidized byproduct [(THF)Na(OOPPh2)]n (4) that can be synthesised directly in high yields in the reaction of Ph2POOH and NaH in THF. 3 was reacted with an equimolar amount of Zn{N(SiMe3)2}2 to give [(Me3Si)2NZnPh2PNSiMe3]2 (5). 3 reacts with caesium under phosphorus-phosphorus bond formation in a reductive substituent coupling reaction to give [(THF)Cs2{Ph(NSiMe3)P}2]n (6) where phosphorus(III) is reduced to phosphorus(II). Phosphorus-phosphorus bond formation to give (Ph2PNSiMe3)2 (7) where the phosphorus(III) centres are oxidized to PIV is observed in the reaction of 3 with n-BuLi and bismuthtrichloride.

Synthese und Reaktivität von Diphenylphosphanyltrimethylsilylamin Ph2PN(H)SiMe3

The 2-pyridyl containing compounds (2-Py)2NH 1, (2-Py)2PH 2, Me2Al(2-Py)2N 3, Me2Al(2-Py)2P 4, Et2Al(2-Py)2N 5, Et2Al(2-Py)2P 6 and Et2Al(2-Py)2NAlEt37 have been synthesized and analyzed by solid state structure determination, FT-Raman spectroscopy and theoretical calculations in order to elucidate the charge density distribution. All di(2-pyridyl) amides and -phosphides coordinate the R2Al+ fragment via both ring nitrogen atoms, but the Lewis basicity of the central two-coordinated nitrogen atom in 5 is high enough to coordinate a second equivalent AlEt3 to form the Lewis acid base adduct Et2Al(2-Py)2NAlEt37. Several density functionals (BLYP, B3LYP, BPW91) have been examined in relation to various basis sets (6-31G, 6-31+G, 6-31G(d), 6-31+G(d)). This computational tool facilitates the unambiguous assignment of the Raman ring vibration frequencies. The shift to higher wavenumbers proceeding from the parent di(2-pyridyl)amine 1 and di(2-pyridyl)-phosphane 2 to the metal complexes 3 and 4 indicates partial double bond localization in the ring positions 3 and 5. This effect is more pronounced in the di(2-pyridyl)amide complexes than in the phosphide. Due to the higher electronegativity of the central nitrogen atom in 3, 5 and 7 compared to the bridging two-coordinated phosphorus atom in 4 and 6 the di(2-pyridyl)amide is the harder Lewis base. In the phosphides nearly all charge density couples into the rings leaving the central phosphorus atom only attractive for soft metals.

Di(2-pyridyl)-Amides and -Phosphides: Syntheses, Reactivity, Structures, Raman-Experiments and Calculations

Starting from tris(benzothiazol-2-yl)phosphane (1) an advanced Janus-head ligand, di(benzothiazol-2-yl)phosphane (2), was synthesised and structurally characterised. The heteroaryl substituents of this ligand provide both hard and soft donor sites. Surprisingly, the phosphorus atom in 2 is divalent and the hydrogen atom is directly bonded to one ring nitrogen atom and hydrogen bonded to the second. Compound 2 decomposes in any common solvent other than diethyl ether and a new preparation to improve the yields of 2 is presented. A coordination polymer, [{Cs(bth)(2)P}8] (3) (bth=benzothiazol-2-yl), was obtained when the sec-phosphane 2 was allowed to react with elemental caesium in a 1:1 ratio in diethyl ether at -78 degrees C. In 3 each anion is coordinated to four caesium cations and vice versa. The central phosphorus atom is coordinated to two metal atoms above and below the mean plane of the anion in positions in which the two lone pairs of a four-electron donor are anticipated. Two additional cations micro-bridge both ring nitrogen atoms. Hence both faces of the Janus-head ligand are coordinated to the same number of metal cations but in a different way.

Di(benzothiazol-2-yl)phosphanide as a Janus-head ligand to caesium.

The (2-Py)2N ligand shows much more conformational freedom than the (2-Py)2P anion in aluminium coordination. The two isomers [Al{(NPy)Py}3] (1a) and [Al{(NPy)Py}2(Py2N)] (1b) were isolated, the former containing exclusively cistrans ligands, and the latter cis-trans ligands together with a trans-trans ligand. The energy differences in the noncoordinated anions (2-Py)2E (E = N, P) were determined by computational methods to be low in the amide. While the N Al

Experimental and Computational Study on a Variety of Structural Motifs and Coordination Modes in Aluminium Complexes of Di(2‐pyridyl)amides and ‐phosphanides

Matthias Pfeiffer

Papers

Phosphane- and phosphorane Janus Head ligands in metal coordination

Synthese und Reaktivität von Diphenylphosphanyltrimethylsilylamin Ph2PN(H)SiMe3

Di(2-pyridyl)-Amides and -Phosphides: Syntheses, Reactivity, Structures, Raman-Experiments and Calculations

Di(benzothiazol-2-yl)phosphanide as a Janus-head ligand to caesium.

Experimental and Computational Study on a Variety of Structural Motifs and Coordination Modes in Aluminium Complexes of Di(2‐pyridyl)amides and ‐phosphanides