Paul J. Ragogna

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.

Donor-acceptor chemistry at heavy chalcogen centers.

A series of coordination complexes, where a heavy chalcogen (Se, Te) acts as the acceptor site, using a variety of electron rich Lewis bases (phosphine, imine, N-heterocyclic carbene), have been synthesized and comprehensively characterized. Each derivative is a representative example of a E-->Ch coordinative bond, characterizing an efficient E-E bond forming methodology and a systematic investigation into the coordination chemistry of the chalcogens. The complexes are susceptible to classic ligand exchange reactions, verifying the dative E-->Ch bonding motif.

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.

Dicationic Sulfur Analogues of N‐Heterocyclic Silylenes and Phosphenium Cations

DABling with sulfur: Sulfur(II) dications can be prepared using alpha-diimines to stabilize the positive charge (see scheme; DAB = diazabutadiene, Dipp = 2,6-diisopropylphenyl, OTf = CF(3)SO(3)). The bonding is best described as that of a N,N-chelated sulfur(II) dication; these species represent the first sulfur-based structural mimics of N-heterocyclic silylene compounds and phosphenium cations.

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.

Remarkably Stable Chalcogen(II) Dications

Air-stable, chalcogen-centered dications have been synthesized and comprehensively characterized. These represent the first diiminopyridine (DIMPY) complexes of the chalcogens as well as the single nonmetallic (sulfur) complex of this ubiquitous ligand. Their stability under ambient conditions is a distinct contrast to other highly charged main-group cations.

Homoleptic pnictogen-chalcogen coordination complexes.

The synthesis and structural characterization of dicationic selenium and tellurium analogues of the carbodiphosphorane and triphosphenium families of compounds are reported. These complexes, [Ch(dppe)][OTf](2) [Ch = Se, Te; dppe = 1,2-bis(diphenylphosphino)ethane; OTf = trifluoromethanesulfonate], are formed using [Ch](2+) reagents via a ligand-exchange protocol and represent extremely rare examples of homoleptic pnictogen → chalcogen coordination complexes. The corresponding arsenic compounds were also prepared, [Ch(dpAse)][OTf](2) [Ch = Se, Te; dpAse = 1,2-bis(diphenylarsino)ethane], exhibiting the first instance of an arsenic → chalcogen dative bond. The electronic structures of these unique compounds were determined and compared to previously reported chalcogen dications.

The direct reaction of the tBu-DAB ligand with SeCl4: a redox route to selenium–nitrogen heterocycles

The reaction of SeCl4 with the ubiquitous tert-butyl-substituted diazabutadiene ligand results in the isolation of a rare example of a 1,2,5-selenadiazolium cation, representing a novel route to Se-N ring formation; these heterocycles can be derivatised at selenium, which has led to the identification of a short Se...N secondary bonding interaction.

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.

Dicationic Tellurium Analogues of the Classic N-Heterocyclic Carbene

The synthesis and comprehensive characterization of the first dicationic tellurium analogues of N-heterocyclic carbenes (NHCs) has been reported, in both the +2 and +4 oxidation states. For the +2 oxidation state, a base-stabilized form of TeCl(2) is used as the starting material. The dications are isolated by means of halide metathesis and the solid-state structures confirm the previously calculated diimine bonding arrangement. For Te(IV), a diamine is used in a high-yielding dehydrohalogen coupling reaction from TeCl(4). The dicationic NHC analogue is isolated in a base-stabilized form through halide abstraction and subsequent coordination by pyridine.