W­(CNAr)6 (CNAr = arylisocyanide) photoreductants catalyze base-promoted homolytic aromatic substitution (BHAS) of 1-(2-iodobenzyl)-pyrrole in deuterated benzene. Moderate to high efficiencies correlate with W­(CNAr)6 excited-state reduction potentials upon one-photon 445 nm excitation, with 10 mol % loading of the most powerful photoreductants W­(CNDipp)6 (CNDipp = 2,6-diisopropyl­phenyl­isocyanide) and W­(CNDippPhOMe3)6 (CNDippPhOMe3 = 4-(3,4,5-trimethoxy­phenyl)-2,6-diisopropyl­phenyl­isocyanide) affording nearly complete conversion. Stern–Volmer quenching experiments indicated that catalysis is triggered by substrate reductive dehalogenation. Taking advantage of the large two-photon absorption (TPA) cross sections of W­(CNAr)6 complexes, we found that photocatalysis can be driven with femtosecond-pulsed 810 nm excitation. For both one- and two-photon excitation, photocatalysis was terminated by the formation of seven-coordinate WII-diiodo [WI2(CNAr)5] complexes. Notably, we discovered that W­(CNDipp)6 can be regenerated by chemical reduction of WI2(CNDipp)5 with excess ligand present in solution.

Table S2. Crystal data and structure refinement for (PPN)2[Fe(phen)(CN-BPh3)4]. ______________________________________________________________________________ Empirical formula C161 H130 B4 Cl2 Fe N8 P4 Formula weight 2470.59 Temperature 100(2) K Wavelength 1.54178 Å Crystal system Monoclinic Space group C2/c Unit cell dimensions a = 21.782(2) Å a= 90°. b = 17.4783(19) Å b= 94.841(7)°. c = 35.354(5) Å g = 90°. Volume 13412(3) Å 3 Z 4 Density (calculated) 1.224 Mg/m 3 Absorption coefficient 2.151 mm -1 F(000) 5168 Crystal size 0.300 x 0.200 x 0.050 mm 3 Theta range for data collection 3.246 to 74.772°. Index ranges -27 ≤ h ≤ 26, -21 ≤ k ≤ 21, -44 ≤ l ≤ 43 Reflections collected 112475 Independent reflections 13749 [R(int) = 0.0780] Completeness to theta = 67.679° 100.0 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 1.

Magnetization dynamics of transition metal complexes manifest in properties and phenomena of fundamental and applied interest (e.g., slow magnetic relaxation in single molecule magnets (SMMs), quantum coherence in quantum bits (qubits), and intersystem crossing (ISC) rates in photophysics). While spin-phonon coupling is recognized as an important determinant of these dynamics, additional fundamental studies are required to unravel the nature of the coupling and thus leverage it in molecular engineering approaches. To this end, we describe here a combined ligand field theory and multireference ab initio model to define spin-phonon coupling terms in S = 2 transition metal complexes and demonstrate how couplings originate from both the static and dynamic properties of ground and excited states. By extending concepts to spin conversion processes, ligand field dynamics manifest in the evolution of the excited state origins of zero-field splitting (ZFS) along specific normal mode potential energy surfaces. Dynamic ZFSs provide a powerful means to independently evaluate contributions from spin-allowed and/or-forbidden excited states to spin-phonon coupling terms. Furthermore, ratios between various intramolecular coupling terms for a given mode drive spin conversion processes in transition metal complexes and can be used to analyze mechanisms of ISC. Variations in geometric structure strongly influence the relative intramolecular linear spin-phonon coupling terms and will thus define the overall spin state dynamics. While of general importance for understanding magnetization dynamics, this study links the phenomenon of spin-phonon coupling across fields of single molecule magnetism, quantum materials/qubits, and transition metal photophysics. File list (2) download file view on ChemRxiv Fe_SPC_MS_rxiv.pdf (4.18 MiB) download file view on ChemRxiv Fe_SPC_SI_rxiv.pdf (3.66 MiB)

We have studied the photochemical cyclization of 1-(2-iodobenzyl)-pyrrole (IBP) and 1-(2-bromobenzyl)-pyrrole (BBP) to 5H-pyrrolo­[2,1-a]­isoindol catalyzed by W­(CNDipp)6 (CNDipp = 2,6-diisopropylphenylisocyanide) in 1,2-difluorobenzene (DFB). Irradiation (445 nm) of W­(CNDipp)6 (5 mol %) in DFB solution converted 78% of IBP (50 mM) to product after 1 h (16 turnovers). Addition of tetra-n-butyl ammonium hexafluorophosphate (TBAPF6) (0.2 M) to the DFB solution led to rapid photoinduced disappearance of W­(CNDipp)6 but, remarkably, did not inhibit photochemical cyclization of IBP, indicating that IBP cyclization could be driven by a nonluminescent photocatalyst.

Thirteen boronated cyanometallates [M(CN-BR 3 ) 6 ] 3/4/5− [M = Cr, Mn, Fe, Ru, Os; BR 3 = BPh 3 , B(2,4,6,-F 3 C 6 H 2 ) 3 , B(C 6 F 5 ) 3 ] and one metalloboratonitrile [Cr(NC-BPh 3 ) 6 ] 3− have been characterized by X-ray crystallography and spectroscopy [UV−vis−near-IR, NMR, IR, spectroelectrochemistry, and magnetic circular dichroism (MCD)]; CASSCF+NEVPT2 methods were employed in calculations of electronic structures. For (t 2g ) 5 electronic configurations, the lowest-energy ligand-tometal charge-transfer (LMCT) absorptions and MCD C-terms in the spectra of boronated species have been assigned to transitions from cyanide π + B−C borane σ orbitals. CASSCF+NEVPT2 calculations including t 1u and t 2u orbitals reproduced t 1u /t 2u → t 2g excitation energies. Many [M(CN-BR 3 ) 6 ] 3/4− complexes exhibited highly electrochemically reversible redox couples. Notably, the reduction formal potentials of all five [M(CN-B(C 6 F 5 ) 3 ) 6 ] 3− anions scale with the LMCT energies, and Mn(I) and Cr(II) compounds, [K(18-crown-6)] 5 [Mn(CN-B(C 6 F 5 ) 3 ) 6 ] and [K(18-crown-6)] 4 [Cr(CN-B(C 6 F 5 ) 3 ) 6 ], are surprisingly stable. Continuous-wave and pulsed electron paramagnetic resonance (EPR; hyperfine sublevel correlation) spectra were collected for all Cr(III) complexes; as expected, 14 N hyperfine splittings are greater for (Ph 4 As) 3 [Cr(NC-BPh 3 ) 6 ] than for (Ph 4 As) 3 [Cr(CN-BPh 3 ) 6 ].