Charles L. B. Macdonald

Cationic Crown Ether Complexes of Germanium(II)

Fit for a king: Cationic complexes of Ge(II) can be prepared by using crown ethers to stabilize and protect the germanium center. Three different crown ethers were employed: [12]crown-4 (see structure, Ge teal, O red, C gray), [15]crown-5, and [18]crown-6. The structures of the cationic complexes depend on the cavity size of the crown ether and on the substituent on germanium.

Experimental and Computational Insights into the Stabilization of Low-Valent Main Group Elements Using Crown Ethers and Related Ligands

A series of tin(II) triflate and chloride salts in which the cations are complexed by either cyclic or acyclic polyether ligands and which have well-characterized single-crystal X-ray structures are investigated using a variety of experimental and computational techniques. Mössbauer spectroscopy illustrates that the triflate salts tend to have valence electrons with higher s-character, and solid-state NMR spectroscopy reveals marked differences between superficially similar triflate and chloride salts. Cyclic voltammetry investigations of the triflate salts corroborate the results of the Mössbauer and NMR spectroscopy and reveal substantial steric and electronic effects for the different polyether ligands. MP2 and DFT calculations provide insight into the effects of ligands and substituents on the stability and reactivity of the low-valent metal atom. Overall, the investigations reveal the existence of more substantial binding between tin and chlorine in comparison to the triflate substituent and provide a rationale for the considerably increased reactivity of the chloride salts.

A Convenient Preparative Method for Cyclic Triphosphenium Bromide and Chloride Salts

Analytically pure chloride and bromide salts of two different cyclic triphosphenium cations are prepared by the reaction of PX3 (X=Cl, Br) in the presence of the halogen-scavenging reagent cyclohexene. For the brominated species, the neutral, volatile 1,2-dibromocyclohexane byproduct is readily removed under reduced pressure, and the desired salts are obtained in high yield. Reactions involving phosphorus trichloride are complicated by the formation of salts containing both chloride and hydrogen dichloride anions. Reactivity experiments on potential undesired halogenated diphosphine byproducts suggest that the formation of such species can be prevented by increasing the concentration of cyclohexene employed in the reaction.

Accessing the Coordination Chemistry of Phosphorus(I) Zwitterions

Go for the gold! Incorporating a borate anion into the backbone of a triphosphenium cation produces a unique zwitterionic phosphanide that can coordinate to one or two {AuCl} fragments depending on the steric bulk of the ligand (see picture; Au yellow, P purple, Cl green). Computational investigations show that in this μ-type ligand, the phosphorus atom behaves only as a σ,π donor.

Reversible, Photoinduced Activation of P4 by Low‐Coordinate Main Group Compounds

Two unique systems based on low-coordinate main group elements that activate P4 are shown to quantitatively release the phosphorus cage upon short exposure to UV light. This reactivity marks the first reversible reactivity of P4, and the germanium system can be cycled 5 times without appreciable loss in activity. Theoretical calculations reveal that the LUMO is antibonding with respect to the main group element-phosphorus bonds and bonding with respect to reforming the P4 tetrahedron, providing a rationale for this unprecedented activity, and suggesting that the process is tunable based on the substituents.

Cross-coupling of aryl/heteroaryl bromides with ammonia using a copper-carbene catalyst

A variety of aryl and heteroaryl bromides were cross-coupled with ammonia in good to high yields in the presence of a copper-NHC catalyst.

Use of a smaller counterion results in an ‘inverse sandwich’ diindium cation

Treatment of In(C 5 Me 5 ) with [(toluene)H[[B(C 6 F 5 ) 4 ] affords the salt [In(η 5 -C 5 Me 5 )In][B(C 6 F 5 ) 4 ]. X-ray analysis indicates that the cation possesses an inverse sandwich structure, one indium atom of which experiences a close contact with a meta -fluorine of a C 6 F 5 group of a [B(C 6 F 5 ) 4 ] − counterion. The other indium atom exhibits a weak η 6 -interaction with a C 6 F 5 group of a different [B(C 6 F 5 ) 4 ] − anion.

Synthesis of Zwitterionic Triphosphenium Transition Metal Complexes: A Boron Atom Makes The Difference

A collection of zwitterionic phosphanide metal carbonyl coordination complexes has been synthesized and fully characterized, representing the first isolated series of metal complexes for the triphosphenium family of compounds. The dicoordinate phosphorus atom of the zwitterion is formally in the +1 oxidation state and can coordinate to one metal, 2M (M = Cr, Mo, W) and 2Fe, or two metals, a Co2(CO)6 fragment 4, depending on the starting reagents. All complexes have been isolated in greater than 80% yield, and structures were confirmed crystallographically. Metrical parameters are consistent with 1 being a weak donor and results in long metal-phosphorus bonds being observed in all cases. Unique bimetallic structures, 3M (M = Cr, Mo, W), consisting of a M(CO)5 fragment on phosphorus and a piano-stool M(CO)3 fragment on a boron phenyl group have been identified in the (31)P{(1)H} NMR spectra and confirmed using X-ray diffraction studies. Use of the borate backbone in 1, which renders the molecule zwitterionic, proves to be a determining factor in whether these metal complexes will form; the halide salt of a cationic triphosphenium ion, 6[Br], shows no evidence for formation of the analogous metal complexes by (31)P{(1)H} NMR spectroscopy, and tetraphenylborate salts, 6[BPh4] and 7[BPh4], produce complexes that are unstable.

Non‐Innocent Ligand Effects on Low‐Oxidation‐State Indium Complexes

Attempts to coordinate neutral ligands to low oxidation state indium centers are often hindered by disproportionation pathways that produce elemental indium and higher oxidation state species. In contrast, we find that reactions of the salt, InOTf (OTf=trifluoromethanesulfonate), with α-diimine ligands yielded intensely colored compounds with no evidence of decomposition. X-ray structural analysis of InOTf⋅(Mes) DAB(Me) ((Mes) DAB(Me) =N,N-dimesityl-2,3-dimethyl-diazabutadiene; 1) reveals a discrete molecular compound with a pyramidal coordination environment at the indium center, consistent with the presence of a stereochemically active lone pair of electrons on indium and a neutral diazabutadiene chelate ligand. The use of the less-electron-rich (Mes) DAB(H) ligand ((Mes) DAB(H) =N,N-dimesityl-diazabutadiene) engenders dramatically different reactivity and produces a metallopolymer (InOTf⋅(Mes) DAB(H) )∞ (2) linked via CC and InIn bonds. The difference in reactivity is rationalized by cyclic voltammetry and DFT studies that suggest more facile electron transfer from In(I) to the (Mes) DAB(H) and bis(aryl)acenaphthenequinonediimine (BIAN) ligands. Solution EPR spectroscopy indicates the presence of non-interacting ligand-based radicals in solution, whereas solid-state EPR studies reflect the presence of a thermally accessible spin triplet consistent with reversible CC bond cleavage.

Azines possessing strong push–pull donors/acceptors

Azines (R(2)C[double bond, length as m-dash]N-N[double bond, length as m-dash]CR(2)) are 2,3-diaza analogues of 1,3-butadiene. In this report we show that strong polarisation of the azine imparts structural features consistent with delocalization within the azine fragment; NLO properties for the azines are also reported.