Phosphine Dissociation Research Articles

Redox-Neutral, Iron-Mediated Directed C-H Activation: General Principles and Mechanistic Insights.

Experimental and computational studies have been conducted and established the general principles for enabling redox-neutral C-H activation by iron(II) complexes. The idealized octahedral iron(II) dimethyl complex, (depe)2Fe(CH3)2 (depe = 1,2-bis(diethylphosphino)ethane) promoted the directed, regioselective ortho C(sp2)-H methylation of pivalophenone. The rate of the iron(II)-mediated C(sp2)-H functionalization depended on the lability of L-type phosphine ligands, the spin state of the iron center, and the size of the X-type ligands (halide, hydrocarbyl) in P4FeIIX2 complexes. The C(sp2)-H alkylation reaction proved general among multiple substrates with directing groups including carbonyl, imines and pyridines. Among these, ketones and aldehydes were identified as optimal and were compatible with various steric environments and presence of acidic α-hydrogens. With stronger nitrogen donors, higher barriers for product-forming reductive elimination were observed. The effect of orbital hybridization on the chemoselectivity of C-H activation through a σ-CAM pathway by dn>0 transition metals was also established by studying the stoichiometric reactivity of the differentially substituted (depe)2Fe(Me)R complexes (R = alkyl, aryl), where the Fe-R bond with greater s-character preferentially promoted selective C-H activation. Deuterium labeling and kinetic studies, coupled with computational analysis, supported a pathway involving phosphine dissociation and rate-determining C-H bond activation, leading to the observed products.

B(C6F5)3 Co-Catalyst Promotes Unconventional Halide Abstraction from Grubbs I to Enhance Reactivity and Limit Decomposition.

Ruthenium based Grubbs metathesis has become a commonplace reaction for synthetic chemists. Development of new generations of catalysts evolving from Grubbs I (GI) have led to greater stability, functional group compatibility, and superior reactivities. However, these advancements lead to increased costs. To this end, we report here how the addition of the commercially available tris(pentafluorophenyl)borane Lewis acid, which has become a common place catalyst in its own right, leads to enhanced reactivity of GI. Moreover, the increased reactivity arises via halide abstraction rather than traditional phosphine dissociation, providing ring-opening metathesis polymerization products that are divergent from those synthesized without the Lewis acid cocatalyst.

α,β‐C—C—C Agostic Bonding Interactions in Ruthenacyclobutane and π‐Complex Assisted Olefin Metathesis Catalyzed by Ruthenium‐Alkylidene Complexes

ABSTRACTComputational aspects of concerted [2+2] oxidative‐retrocycloaddition‐cycloreversion reaction through ruthenium alkylidene π‐complexes and ruthenacyclobutane with α,β‐(C—C—C) agostic bonding interactions in olefin metathesis are presented. d6‐Ruthenium carbene complexes, with ruthenium in the oxidation state +2, undergo successive [2+2] cycloaddition and cycloreversion steps, through associative, dissociative, or interchange mechanisms. This process involves coordination of the olefin to 16‐electron Ru complex followed by phosphine dissociation, or first phosphine dissociation then coordination of the olefin to the 14‐electron Ru complex with rearrangement to a ruthenacyclobutane intermediate, followed by symmetrical reverse steps. Donation of σ‐electron density from the two C—C σ‐bonds to the metal center leads to α,β‐(C—C—C) agostic bonds, which stabilized metallacyclobutane as a formally 16‐electron complex, with lower energy than the corresponding π‐complex. In the transformation from π‐complex to ruthenacyclobutane the ruthenium atom is formally oxidized to Ru(IV). The most efficient ligands are those that stabilize the high‐oxidation state metallacyclobutane (IV) intermediate relative to the ruthenium carbene.

Ruthenium(II) complexes of a tripodal phosphite ligand: Synthesis, characterization, and applications in catalytic dehydrogenation

The scaffold tris(8-quinolinyl)phosphite, (P(Oquin)3), can bind to metal centers as a bi- or a tridentate tripodal ligand, depending on the synthetic conditions and characteristics of the metal atom. Here the study of the coordinating properties of such chelate was extended to the synthesis and characterization of well-defined Ru(II)-halide complexes. The compound [κ3(N,P,N){P(Oquin)3}RuCl2(PPh3)] was obtained by simple ligand exchange on the precursor [(PPh3)3RuCl2]. Two isomers were observed by means of 31P{1H} NMR spectroscopy, and were partially separated by recrystallization in refluxing solvents, thus allowing their structure elucidation. X-ray diffraction analysis revealed that the two crystalline isomers have the formula [κ3(N,P,N){P(Oquin)3}RuCl2(PPh3)] with the phosphite ligand coordinated to the Ru(II) center either in a meridional or in a facial disposition. The mixture [κ3(N,P,N){P(Oquin)3}RuCl2(PPh3)] undergoes phosphine dissociation at temperatures over 100 °C, leading to the formation of [κ4(P,N3){P(Oquin)3}RuCl2]. This compound displays a tetradentate P(Oquin)3 chelate and is a suitable catalyst for the dehydrogenation of formic acid and the dehydrocoupling of methylphenylsilane.

Reductive Elimination Reactions in Gold(III) Complexes Leading to C(sp3)-X (X = C, N, P, O, Halogen) Bond Formation: Inner-Sphere vs SN2 Pathways.

The reactions leading to the formation of C-heteroatom bonds in the coordination sphere of Au(III) complexes are uncommon, and their mechanisms are not well known. This work reports on the synthesis and reductive elimination reactions of a series of Au(III) methyl complexes containing different Au-heteroatom bonds. Complexes [Au(CF3)(Me)(X)(PR3)] (R = Ph, X = OTf, OClO3, ONO2, OC(O)CF3, F, Cl, Br; R = Cy, X = Me, OTf, Br) were obtained by the reaction of trans-[Au(CF3)(Me)2(PR3)] (R = Ph, Cy) with HX. The cationic complex cis-[Au(CF3)(Me)(PPh3)2]OTf was obtained by the reaction of [Au(CF3)(Me)(OTf)(PPh3)] with PPh3. Heating these complexes led to the reductive elimination of MeX (X = Me, Ph3P+, OTf, OClO3, ONO2, OC(O)CF3, F, Cl, Br). Mechanistic studies indicate that these reductive elimination reactions occur either through (a) the formation of tricoordinate intermediates by phosphine dissociation, followed by reductive elimination of MeX, or (b) the attack of weakly coordinating anionic (TfO- or ClO4-) or neutral nucleophiles (PPh3 or NEt3) to the Au-bound methyl carbon. The obtained results show for the first time that the nucleophilic substitution should be considered as a likely reductive elimination pathway in Au(III) alkyl complexes.

Molecular Motion in the Interconverting σ-H2, Di-, and Tri-hydride Regimes: .

The transition-metal complex is known to exist in three possible isomeric forms, including a nonclassical, σ-bound dihydrogen complex and two classical dihydride isomers. As such, it has served as a model complex for the energies of conversion between these limiting structural regimes. In the present study, ab initio molecular dynamics computer simulations, combined with enhanced sampling techniques, were utilized to directly assess the degree of motion and isomerization of the dihydrogen/dihydride moieties in this complex. Ligand rotations (for both the H2 unit and the phosphine units) were found to be dominant in the low-temperature (298 K) regime, and the classical thermodynamic distribution showed no probability of thermally accessing dihydride forms, although unrestrained molecular dynamics trajectories showed fleeting configurations outside of the σ-H2 configuration. Simulations at higher temperatures surprisingly revealed new tri-hydride isomers that are energetically competitive with the σ-H2 and cis-/trans-dihydride isomers. Low-energy pathways to hydrogen/hydride transfer and phosphine dissociation were readily accessible, which considerably expands the known isomeric flexibility of this complex.

The Labile Nature of Air Stable Ni(II)/Ni(0)-phosphine/Olefin Catalysts/Intermediates: EDA-NOCV Analysis.

Metal ions-based inorganic-organic hybrid composites are often reported acting as good to excellent catalysts with various substrate scopes under milder reaction conditions. The active catalyst of a catalytic cycle is sometimes proposed to be a short-lived reactive intermediate species. A three coordinate (L-Me)Ni(II) intermediate species [L-Me=O2 N donor dianionic ligand] can bind with short-lived carbene-ester ligands to produce four coordinate Ni(II) species which can act as carbene transfer intermediate under suitable reaction conditions for C-H functionalization and/or cyclopropanation reactions. The dissociation of phosphine (PPh3 ) from the Ni(II) centre of (L-Me)Ni(II)(PPh3 ) (1 a) and binding of short lived carbene esters (:CR1 -CO2 R2 ; R1 =H, Ph; R2 =aliphatic group; 2-4 and other carbenes; 5-10) to Ni(II) rationalize the phenomenon in solution. Air stable Ni(0)-olefin complexes/intermediates (12-18) have recently been shown to mediate a variety of organic transformations. This analysis will further help organic/organometallic chemists to rationalize the design and synthesis of future catalysts for organic transformation. EDA-NOCV calculations have been performed to shed light on the stability and bonding of those species. Additionally, our analysis provides a proper reason why the analogous (L-Me)Pd-PPh3 complex (1 b) does not dissociate in solution and hence, a similar catalytic product has not been isolated from identical reaction conditions. The stability and the labile nature of Ni(II/0) complexes have been investigated by state-of-the-art EDA-NOCV analyses.

A Ruthenium Protic N-Heterocyclic Carbene Complex as a Precatalyst for the Efficient Transfer Hydrogenation of Aryl Ketones

A neutral azole precursor to a protic N-heterocyclic carbene (pNHC) ligand, 6-((4,5-diphenyl-1H-imidazol-1-yl)methyl)-2,2′-bipyridine (3), was prepared from 6-(bromomethyl)-2,2′-bipyridine (2) and 4,5-diphenylimidazole. Complex [RuCl(pNHC-bpy)(PPh3)2](PF6) (4) bearing a protic, bipyridine-tethered NHC ligand was prepared by refluxing 3 with RuCl2(PPh3)3 and KPF6 in methanol and was characterized by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, elemental analysis, and a single-crystal X-ray diffraction study. The hydrido complex [RuH(pNHC-bpy)(PPh3)2](PF6) (5) was prepared by reaction of 4 with NaBH4 in ethanol and characterized by NMR and Fourier transform infrared spectroscopy. Complex 5 was used as the catalyst (0.1 mol % loading) in the transfer hydrogenation of a range of alkyl/aryl ketones in basic iso-propanol at 60 °C. Bulky alkyl groups or ortho-substituted aryl groups at the ketones slowed down or inhibited the catalytic transformation. The addition of an excess of triphenylphosphine also slowed the catalysis, providing an indication for a mechanism involving phosphine dissociation, while the addition of an excess of elemental mercury had only a small effect on the conversion. The importance of potassium cations in the mechanism is consistent with the observation of reduced catalytic conversion when [2,2,2]-cryptand was present or when 1,8-diazabicyclo[5.4.0]undec-7-ene was used as the base. A plausible homogeneous catalysis mechanism involving the innersphere addition of hydride to the substrate in the transition state TS1 is supported by density functional theory calculations where the potassium ion has replaced the hydrogen atom of the N–H group in a protic NHC.

Comparing the Electronic Structure of Iron, Cobalt, and Nickel Compounds That Feature a Phosphine-Substituted Bis(imino)pyridine Chelate

It was recently discovered that (Ph2PPrPDI)Mn (PDI = pyridine diimine) exists as a superposition of low-spin Mn(II) that is supported by a PDI dianion and intermediate-spin Mn(II) that is antiferromagnetically coupled to a triplet PDI dianion, a finding that encouraged the synthesis and electronic structure evaluation of late first row metal variants that feature the same chelate. The addition of Ph2PPrPDI to FeBr2 resulted in bromide dissociation and the formation of [(Ph2PPrPDI)FeBr][Br]. Reduction of this precursor using excess sodium amalgam afforded (Ph2PPrPDI)Fe, which possesses an Fe(II) center that is supported by a dianionic PDI ligand. Similarly, reduction of a premixed solution of Ph2PPrPDI and CoCl2 yielded the cobalt analog, (Ph2PPrPDI)Co. EPR spectroscopy and density functional theory calculations revealed that this compound features a high-spin Co(I) center that is antiferromagnetically coupled to a PDI radical anion. The addition of Ph2PPrPDI to Ni(COD)2 resulted in ligand displacement and the formation of (Ph2PPrPDI)Ni, which was found to possess a pendent phosphine group. Single-crystal X-ray diffraction, CASSCF calculations, and EPR spectroscopy indicate that (Ph2PPrPDI)Ni is best described as having a Ni(II)-PDI2- configuration. The electronic differences between these compounds are highlighted, and a computational analysis of Ph2PPrPDI denticity has revealed the thermodynamic penalties associated with phosphine dissociation from 5-coordinate (Ph2PPrPDI)Mn, (Ph2PPrPDI)Fe, and (Ph2PPrPDI)Co.

Kinetics of halide exchange in cyclopentadienylruthenium bis(triarylphosphine)halides

The kinetics of halide exchange in cyclopentadienylruthenium bis(triarylphosphine) halide complexes CpRu(PAr3)2X (1a X = Cl, 1b X = Br, 1c X = I; X′= Cl, Br, Ar = C6H5, 2 Ar = p-CH3OC6H4, X = Cl, X′= Br and 3 Ar = p-FC6H4, X = Cl, X′ = Br) have been measured and the results interpreted with respect to two possible mechanisms: halide dissociation vs phosphine dissociation. Halide exchange between nBu4NX′ and 1–3 in fluorobenzene under pseudo-first order conditions is found to be first order in 1–3. Relative rates of halide exchange follow the order: 1a > 1b > 1c > 2 ≈ 3 with activation parameters ΔH† = 117 ± 6 kJ/mol and ΔS† = 44 ± 18 J/mol-K (1a, X′ = Br) and ΔH† = 120 ± 14 kJ/mol ΔS† = 50 ± 45 J/mol-K (1b, X′ = Cl). Plots of kobs vs [X′–] for 1 and 2 are consistent with a two-term rate law where kobs = (k1 + k2[X′–]) while reactions of 3 are independent of the halide concentration. The rate data are consistent with phosphine dissociation as the rate determining step followed by a slightly faster reaction with halide ions where the dissociated phosphine competes effectively with halide for the open coordination site in a CpRu(PAr3)X intermediate.

An Au8 Cluster Fortified by Four Ferrocenes.

Atomically precise metal clusters are now in the research spotlight, owing to the precise correlation between the physicochemical properties and their atomic-packing structures at an atomic-level. Herein we synthesized an Au8 cluster capped by four ferrocene ligands (DPPF), in which the ferrocene not only can direct the precise formation of the Au8 cluster, but also can solidify the structural pattern of the Au8 cluster. The Au8(DPPF)4 clusters as heterogeneous catalysts can achieve efficiently catalytic performances for the CO oxidation reaction, mainly due to the resistance to aggregation into large particles under reaction conditions. Our results suggest that the homolytic phosphine dissociation nature and the postdissociation reconstruction effect induced by Fe may enhance the catalytic performances of Au8(DPPF)4.

Rate-Limiting Steps in the Intramolecular C-H Activation of Ruthenium N-Heterocyclic Carbene Complexes.

Ruthenium (II) complexes with N-heterocyclic carbenes (NHC) are commonly used as efficient catalysts in hydrogenation of olefins with simultaneous intramolecular C–H activation. Using the DFT approach, we have investigated the entire hydrogenation reaction pathway for four new potential catalysts and ethylene, a model substrate. Our calculations imply that the dissociation of phosphine is the rate-limiting step of hydrogenation, contrary to recent computational results. We also found that catalysts bearing NHCs with aliphatic and aromatic side groups are energetically favorable over other aliphatic cyclohexyl-substituted NHC. To examine how electronic properties of various catalysts influence the energetic barrier in the crucial steps of the reaction, we applied the Noncovalent Interaction analysis, which allowed us to reveal crucial interactions which stabilize/destabilize important intermediates and transition states in the hydrogenation reaction.

Ru0 or RuII: A Study on Stabilizing the "Activated" Form of Ru-PNP Complexes with Additional Phosphine Ligands in Alcohol Dehydrogenation and Ester Hydrogenation.

The complex Ru-MACHO has been previously shown to undergo uncontrolled degradation subsequent to base-induced dehydrochlorination in the absence of a substrate. In this study, we report that stabilization of the dehydrochlorinated Ru-MACHO with phosphines furnishes complexes whose structures depend on the phosphines employed: while PMe3 led to the expected octahedral RuII complex, PPh3 provided access to a trigonal-bipyramidal Ru0 complex. Because both complexes proved to be active in base-free (de)hydrogenation reactions, thorough quantum-chemical calculations were employed to understand the reaction mechanism. The calculations show that both complexes lead to the same mechanistic scenario after phosphine dissociation and, therefore, only differ energetically in this step. According to the calculations, the typically proposed metal-ligand cooperation mechanism is not the most viable pathway. Instead, a metal-ligand-assisted pathway is preferred. Finally, experiments show that phosphine addition enhances the catalyst's performance in comparison to the PR3-free "activated" Ru-MACHO.

Combined Experimental and Theoretical Study on Hampered Phosphine Dissociation in Heteroleptic Ni/Zn Complexes.

Heterometallic Ni/Zn complexes can serve as molecular models for the semihydrogenation of acetylene catalyzed by heterogeneous Ni/Zn phases. Pursuing this target, we present the synthesis of the series [Ni(ZnCp*)n(ZnMe)n(PEt3)4-n] (n = 1-3; 1, 2, 3) which is obtained via E/Zn exchange from [Ni(ECp*)n(PEt3)4-n] (n = 1-3, E = Al, Ga; P1, P2, P3). The isolation of the intermediate compound [Ni(GaCp*)(ZnCp*)(ZnMe)(PEt3)2] (2a) supports the assumption of a stepwise Ga/Zn exchange in the formation of 3. The dissociation behavior of PEt3 in 2 and 3 was investigated experimentally using variable temperature (VT) UV-vis spectroscopy indicating suppressed phosphine dissociation in both cases. For comparison, the absorption spectra of the saturated and unsaturated compounds were calculated using time dependent DFT calculations (TDDFT). Energy decomposition analysis with the natural orbital for chemical valence extension (EDA NOCV) calculations shows a bond strengthening of the Ni-P bond by successive substitution of the phosphines with (ZnR)2 units. The influence of different phosphines (PMe3, PEt3, PPh3, P(OEt)3) on Ni-P bond length and on Zn-Zn interactions in [Ni(ZnR)2n(PR')4-n] (R = Cp*, Me; R' = Me, Et, Ph, OEt) was also studied by DFT calculations. A correlation of increasing sterical demand of the phosphine ligand and a shortening of the Zn-Zn distances is observed.

Frustrated Lewis Pair Chemistry Enables N2 Borylation by Formal 1,3-Addition of a B-H Bond in the Coordination Sphere of Tungsten.

The first example of a formal 1,3-B-H bond addition across the M-N≡N unit of an end-on dinitrogen complex has been achieved. The use of Piers' borane HB(C6 F5 )2 was essential to observe this reactivity and it plays a triple role in this transformation: 1) electrophilic N2 -borylation agent, 2) Lewis acid in a frustrated Lewis pair-type B-H bond activation, and 3) hydride shuttle to the metal center. This chemistry is supported by NMR spectroscopy and solid-state characterization of products and intermediates. The combination of chelate effect and strong σ donation in the diphosphine ligand 1,2-bis(diethylphosphino)ethane was mandatory to avoid phosphine dissociation that otherwise led to complexes where borylation of N2 occurred without hydride transfer.

Ligands Based on Phosphine-Stabilized Aluminum(I), Boron(I), and Carbon(0).

A systematic quantum chemical study of the bonding in d6 -transition-metal complexes, containing phosphine-stabilized, main-group-element fragments, (R3 P)2 E, as ligands (E=AlH, BH, CH+ , C), is reported. By using energy decomposition analysis, it is demonstrated that a strong M-E bond is accompanied by weak P-E bonds, and vice versa. Although the Al-M bond is, for example, found to be very strong, the weak Al-P bond suggests that the corresponding metal complexes will not be stable towards phosphine dissociation. The interaction energies for the boron(I)-based ligand are lower, but still higher than those for two-carbon-based ligands. For neutral ligands, electrostatic interactions are the dominating contributions to metal-ligand bonding, whereas for the cationic ligand a significant destabilization, with weak orbital and even weaker electrostatic metal-ligand interactions, is observed. Finally, for iron(II) complexes, it is demonstrated that different reactivity patterns are expected for the four donor groups: the experimentally observed reversible E-H reductive elimination of the borylene-based ligand (E=BH) exhibits significantly higher barriers for the protonated carbodiphosphorane (CDP) ligand (E=CH) and would proceed through different intermediates and transition states. For aluminum, such reaction pathways are not feasible (E=AlH). Moreover, it is demonstrated that the metal hydrido complexes with CDP ligands might not be stable towards reduction and isomerization to a protonated CDP ligand and a reduced metal center.

The activity of indenylidene derivatives in olefin metathesis catalysts.

The first turnover event of an olefin metathesis reaction using a new family of homogenous Ru-based catalysts bearing modified indenylidene ligands has been investigated, using methoxyethylene as a substrate. The study is carried out by means of density functional theory (DFT). The indenylidene ligands are decorated with ortho-methyl and isopropyl groups at both ortho positions of their phenyl ring. DFT results highlight the more sterically demanding indenylidenes have to undergo a more exothermic first phosphine dissociation step. Overall, the study emphasises advantages of increased steric hindrance in promoting the phosphine release, and the relative stability of the corresponding metallacycle over classical ylidene ligands. Mayer bond orders and steric maps provide structural reasons for these effects, whereas NICS aromaticity and conceptual DFT confirm that the electronic parameters do not play a significant role.

Mechanism of copper-free Sonogashira reaction operates through palladium-palladium transmetallation

The seminal contributions by Sonogashira, Cassar and Heck in mid 1970s on Pd/Cu- and Pd-catalysed (copper-free) coupling of acetylenes with aryl or vinyl halides have evolved in myriad applications. Despite the enormous success both in academia and in industry, however, critical mechanistic questions of this cross-coupling process remain unresolved. In this study, experimental evidence and computational support is provided for the mechanism of copper-free Sonogashira cross-coupling reaction. In contrast to the consensus monometallic mechanism, the revealed pathway proceeds through a tandem Pd/Pd cycle linked via a multistep transmetallation process. This cycle is virtually identical to the Pd/Cu tandem mechanism of copper co-catalysed Sonogashira cross-couplings, but the role of CuI is played by a set of PdII species. Phosphine dissociation from the square-planar reactants to form transient three-coordinate Pd species initiates transmetallation and represents the rate-determining step of the process.

Suppressed Phosphine Dissociation by Polarization Effects on the Donor–Acceptor Bonds in [Ni(PEt3)4–n(ECp*)n] (E = Al, Ga)

A series of heteroleptic complexes [Ni(PEt3)4- n(ECp*) n] (E = Al, Ga, Cp* = pentamethylcyclopentadienyl, n = 0-4) was prepared and characterized by experimental as well as computational means. The series of compounds was studied with respect to ligand dissociation processes which are fundamental for reactivity. In contrast to the homoleptic complexes [Ni(PR3) n] phosphine dissociation is remarkably suppressed in the heteroleptic title complexes. Single crystal X-ray structures as well as density functional theory calculations reveal a gradual decrease of the Ni-PEt3 distances with increasing number of coordinated group-13 ligands ECp*. Accordingly, variable-temperature UV-vis studies of [Ni(PEt3)4- n(AlCp*) n] in solution indicate no ligand dissociation equilibrium for n ≥ 2. Energy decomposition analysis with the natural orbital for chemical valence extension shows higher Ni-P interaction energies for [Ni(PEt3)4- n(AlCp*) n] than for [Ni(PEt3)4] which is mainly a result of an increase in columbic attraction forces induced by Ni-PEt3 bond polarization upon ECp* coordination.

Solution state fluxionality and thermolysis reactions of bimetallic single source precursors for I-III-VI chalcopyrite materials

Complexes of the type (PPh3)2M(μ-SEt)2E(SEt)2 (M = Cu, Ag; E = Al, Ga, In) are effective and versatile molecular precursors for bimetallic and mixed MES2 chalcopyrite nanomaterials. In solution at room temperature, these compounds exhibit spectroscopic characteristics inconsistent with their cyclic solid state structures, and variable temperature NMR investigations in this report show that this discrepancy is a result of rapid exchange of thiolate groups between bridging and terminal positions. These experiments show that the exchange is unimolecular and does not involve phosphine dissociation or free thiol. Exchange rates are not strongly affected by thiolate electronic properties or the identity of E, but are significantly slower for more sterically demanding phosphine and thiolate ligands. Data are consistent with a simple turnstyle exchange mechanism involving dissociation of one bridging thiolate ligand from M, although crossover studies suggest that full ionic dissociation (into [(PPh3)2M][E(SEt)4]) is also facile, and that dissociation into neutral fragments (PPh3)2MSEt + E(SEt)3 may proceed at higher temperatures. Additional investigation of the solution state thermolyses of the same complexes demonstrates that the processes above do not correlate to their decomposition behavior, as thermal sensitivity is most strongly effected by thiolate electronic properties, and likely depends most strongly on cleavage of CS bonds.