Chromium Pentacarbonyl-Substituted Organotin(II) Cation Stabilized

Article pubs.acs.org/Organometallics

Chromium Pentacarbonyl-Substituted Organotin(II) Cation Stabilized by p‑Dimethylaminopyridine or Triphenylphosphane Oxide† Michael Wagner, Markus Henn, Christina Dietz, Markus Schürmann, Marc H. Prosenc,§ and Klaus Jurkschat* Lehrstuhl für Anorganische Chemie II, Technische Universität Dortmund, 44221 Dortmund, Germany S Supporting Information *

ABSTRACT: The syntheses of the heteroleptic organostannylene chromium pentacarbonyl complexes [4-t-Bu-2,6-{P(O)(Oi-Pr)2}2C6H2(X)SnCr(CO)5] (2, X = ClO4; 3, X = OTf) and [4-t-Bu-2,6-{P(O)(Oi-Pr)2}2C6H2(L)SnCr(CO)5][ClO4] (4, L = p-Me2NC5H4N; 5, L = Ph3PO) are reported. In complex 2, as its toluene solvate 2·C7H8, and 3, as its toluene solvate 3·0.5C7H8, the perchlorate and triflate anions coordinate the tin atom at Sn−O distances of 2.170(3) and 2.178(3) Å, respectively. In the complexes 4 and 5, however, the perchlorate anion is displaced from the tin atom by the 4-dimethylaminopyridine and triphenylphosphane oxide donor, respectively, to give salt-like solid-state structures. In addition to the single-crystal X-ray diffraction studies all compounds were characterized by multinuclear NMR and IR spectroscopy, electrospray mass spectrometry, and elemental analysis. DFT calculations with subsequent NBO analyses reveal the bonding of both the 4-dimethylaminopyridine and triphenylphosphane oxide to be donor−acceptor-like with charge transfer from these donor molecules to the tin atoms.

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is indeed the case for X = perchlorate, ClO4−, and triflate, CF3SO3−, as shown below.

INTRODUCTION In recent years, the interest in subvalent tin cations has intensified.1 This growing interest is traced to the potential such compounds hold as strongly Lewis-acidic catalysts for organic reactions.1b,d Compared to the great variety of Sn(IV) cation-based catalysts,2a this potential has been explored much less. One way to stabilize electrophilic Sn(II) moieties is to react them with a Lewis base, e.g., 4-dimethylaminopyridine, pMe2NC5H4N, hereafter referred to as DMAP. Representative examples are shown in Chart 1. Jutzi et al. reported the Cp*Sn+ cation A and its pyridine/ bipyridine B/C adducts.2b,c,3 Also reported were the intramolecularly coordinated ammonium-type structure D4 and the Lewis base-stabilized chromium pentacarbonyl complexes of organotin cations E and F.5 Very recently Jones and Krossing published the tin amide cation G and its adduct with DMAP H.6 Anionic N-donor ligands were used by Fulton (J)8 and Kawashima (K).9 Stalke and Roesky described the autoionization of SnCl2 with a neutral donor ligand (L, M).10,11 Crown ethers also proved to be capable of stabilizing tin(II) cations.13 Last but not least, a remarkable tin dication of type N that is stabilized by transfer of π-electron density from aromatic rings to the electron-deficient tin center has been reported by Müller et al.12 In the course of our ongoing studies on the synthesis and reactivity of intramolecularly coordinated heteroleptic organostannylenes14 of the type [R(X)SnM(CO)5] (R = 4-t-Bu-2,6[P(O)(Oi-Pr)2]2C6H2, X = electronegative substituent, M = Cr, Mo, W) we envisioned that the addition of a strong Lewis base to a stannylene complex containing a good leaving group X would furnish the desired base-stabilized salt-like complex. This © 2013 American Chemical Society

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RESULTS AND DISCUSSION The reaction of [R(Cl)SnCr(CO)5], 1 (R = 4-t-Bu-2,6[P(O)(Oi-Pr)2]2C6H2), with silver perchlorate provided the corresponding perchlorate derivative 2, which crystallized from toluene as its colorless toluene solvate 2·C7H8 (Scheme 1). In a similar manner, the triflate derivative 3 was obtained, as its toluene solvate 3·0.5C7H8, by the reaction of 1 with silver triflate, AgOTf (Scheme 1). Compounds 2·C 7 H 8 and 3·0.5C7H8 are respectively light green and colorless crystalline materials that are well soluble in common organic solvents such as toluene, tetrahydrofuran, and diethyl ether. The molecular structure of 2·C7H8 is shown in Figure 1, and that of 3·0.5C7H8 in Figure 2. Selected bond lengths and angles are given in Table 1. In both 2·C7H8 and 3·0.5C7H8 the Sn(1) atom exhibits a strongly distorted trigonal bipyramidal configuration with O(1) and O(2) occupying the axial positions, whereas the equatorial positions are taken by the C(1), O(21) (2·C7H8)/O(3) (3·0.5C7H8), and Cr(1) atoms. The deviation from the ideal geometry is especially manifested by the O(1)−Sn(1)−O(2) angle of 155.0(1)° (2·C7H8)/155.8(1)° (3·0.5C7H8), being the result of ligand constraint, and the C(1)−Sn(1)−Cr(1) angle of 146.3(1)° (2·C7H8)/153.3°(1) (3·0.5C7H8). The perchlorate and triflate anions coordinate the tin atom at Sn(1)− O(21) and Sn(1)−O(3) distances of 2.170(3) and 2.178(3) Å, Received: February 14, 2013 Published: April 2, 2013 2406

dx.doi.org/10.1021/om400131v | Organometallics 2013, 32, 2406−2415

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Chart 1. Subvalent Tin Cations and Their Lewis Base Adducts

F 4C 6 HCO 2 ) 4 ·ClO 4 }·{O 2 CC 6 HF 4 }] (R = o-F-C 6 H 4 CH 2 ) [2.089 Å]16 and [Sn(tpp)(ClO4)2] (tpp = tetraphenylporphinato) [2.181 Å].17A comparable Sn−O distance of 2.1486(13) Å was observed in the stannylene transition metal complex LSn(OTf)Fe(CO)4 (L = CH{CMe(NAr)}2, Ar = 2,6-iPr2C6H3).18 The structures of compounds 2·C7H8 and 3·0.5C7H8 are rather similar to that of the chlorido-substituted compound 1.14d The main differences are the larger C(1)− Sn(1)−Cr(1) angles of 146.3(1)° (2·C7H8) and 153.3(1)° (3·0.5C7H8) as compared to 1 (141.2(1)°). This is in line with the chloride ligand having the strongest donor capacity. The 31P NMR spectra of compound 2 (in C6D6) and 3 (in C7D8) showed singlet resonances at δ 30.8 (J(31P−117/119Sn) = 185/194 Hz) and 30.2 (J( 31 P− 117/119 Sn) = 189 Hz, unresolved), respectively. The 119Sn NMR spectra displayed triplet resonances at δ 81 (J(119Sn−31P) = 194 Hz, 2) and 71 (J(119Sn−31P) = 193 Hz, 3). The 1H NMR spectra exhibited broad unresolved signals that did not sharpen on lowering the temperature. This might be a hint that dynamic processes are taking place, which, however, were not investigated further. The electrospray mass spectrum (positive mode) of compound 2 showed mass clusters centered at m/z = 814 and 773 that are assigned to [M − ClO4− + CH3CN]+ and [M − ClO4−]+, respectively. These data suggest that the formation of salt-like

Scheme 1. Synthesis of Compounds 2−5

respectively. Coordinating triflate moieties are common in stannylene compounds.15 Similar distances were observed for the tin(IV) derivatives [{(SnR)3(OH)(2,3,4,52407


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Figure 1. General view (SHELXTL) of a molecule of 2·C7H8 showing 30% probability displacement ellipsoids. The hydrogen atoms and the toluene solvate molecule are omitted for clarity.

Figure 2. General view (SHELXTL) of a molecule of 3·0.5C7H8 showing 30% probability displacement ellipsoids. The hydrogen atoms and the toluene solvate molecule are omitted for clarity.

species is possible and that their isolation might be realized by choosing an appropriate donor ligand.

Addition of DMAP to a solution of compound 1 in C6D6 or CD3CN has no effect at all on the magnitude of the 2408


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Table 1. Selected Experimental and Calculated Bond Lengths (Å) and Angles (deg) for Compounds 2·C7H8, 3·0.5C7H8, 4, and 5 Sn(1)−C(1) Sn(1)−Cr(1) Sn(1)−X Sn(1)−O(1) Sn(1)−O(2) P(1)−O(1) P(1)−O(1′) P(1)−O(1″) P(2)−O(2) P(2)−O(2′) P(2)−O(2″) Cr(1)−Sn(1)−C(1) Cr(1)−Sn(1)−X C(1)−Sn(1)−X O(1)−Sn(1)−O(2) C(1)−C(2)−P(1) C(1)−C(6)−P(2)

2·C7H8, X = O(21)

2 (calcd)

3·0.5C7H8, X = O(3)

4, X = N(30)

4 (calcd)

5, X = O(3)

5 (calcd)

2.167(4) 2.5732(7) 2.170(3) 2.291(3) 2.347(3) 1.494(3) 1.566(3) 1.556(3) 1.494(3) 1.551(3) 1.572(3) 146.3(1) 125.46(7) 87.7(1) 154.97(9) 114.6(3) 115.6(3)

2.213 2.614 2.195 2.377 2.374 1.514 1.586 1.595 1.514 1.595 1.586 149.3 128.1 82.6 156.1 115.7 115.7

2.176(3) 2.5546(6) 2.178(3) 2.322(2) 2.332(2) 1.494(3) 1.549(3) 1.561(3) 1.496(2) 1.553(2) 1.563(2) 153.30(9) 118.11(8) 88.6(1) 155.82(9) 115.4(3) 115.6(3)

2.157(3) 2.5744(6) 2.166(3) 2.300(2) 2.325(2) 1.489(2) 1.554(3) 1.543(3) 1.486(2) 1.554(3) 1.558(3) 137.22(9) 123.54(7) 99.2(1) 150.65(8) 114.8(3) 115.2(3)

2.204 2.611 2.286 2.370 2.402 1.523 1.568 1.598 1.520 1.576 1.597 142.5 111.3 106.1 148.3 115.9 115.6

2.151(3) 2.5660(5) 2.104(2) 2.269(2) 2.358(2) 1.485(2) 1.548(2) 1.555(2) 1.490(2) 1.541(2) 1.569(2) 158.55(7) 112.91(6) 88.38(9) 156.53(7) 114.4(2) 115.3(2)

2.221 2.627 2.160 2.367 2.393 1.518 1.583 1.592 1.518 1.579 1.595 141.5 124.0 94.5 153.8 115.8 115.7

Figure 3. General view (SHELXTL) of a molecule of 4 showing 30% probability displacement ellipsoids. The hydrogen atoms are omitted for clarity.

J(31P−117/119Sn) coupling constant. It illustrates the poor leaving capacity of the chloride anion. The reaction of compound 2 with DMAP and triphenylphosphane oxide, Ph3PO, in toluene provided the corresponding donor-stabilized organotin(II) perchlorate salts 4 and 5, respectively (Scheme 1), in moderate isolated yields as colorless single-crystalline materials. Both compounds show good solubility in CH2Cl2. They are sparingly soluble in benzene and toluene. The molecular structures of compounds 4 and 5 are depicted in Figures 3 and 4, respectively. Selected bond lengths and angles are given in Table 1. Both compounds are clearly ionic with Sn(1)···O distances of 5.034(4) (4) and 7.209(3) (5) Å. As in 2·C7H8 and 3·0.5C7H8,

the Sn(1) atom in 4 exhibits a strongly distorted trigonal bipyramidal configuration with O(1) and O(2) occupying the axial positions and the C(1), Cr(1), and N(30) atoms being located in the equatorial positions. The C(1)−Sn(1)−Cr(1) angle of 137.2(1)° is considerably smaller than in the organotin perchlorate derivative 2·C7H8. The Sn(1)−N(30)−C(33) angle of 169.1(1)° is similar to the corresponding angle of 168.0(1)° observed for [Ar*(Me3Si)NSn(DMAP)][Al{OC(CF3)3}4] (Ar* = C6H2{C(H)Ph2}2Me-2,6,4; see G in Chart 1).6 The Sn(1)−N(30) distance of 2.166(3) Å is shorter than in the latter compound [2.286(6) Å]6 and in the intramolecularly coordinated organotin cation [2,6-(Me2NCH2)2C6H3(H2O)SnW(CO)5]+ [2.264(2) Å]4 as well as in [Cp*SnNC5H5]+ 2409


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Figure 4. General view (SHELXTL) of a molecule of 5 showing 30% probability displacement ellipsoids. The hydrogen atoms are omitted for clarity.

[2.691 Å],3 indicating the tin atom in compound 4 to be rather Lewis-acidic. The Sn(1) atom in the triphenylphosphane oxide complex 5 shows a distorted square pyramidal configuration with the C(1), Cr(1), O(1), and O(2) atoms forming the square and the O(3) atom taking the apical position. The Sn(1)−O(3) distance of 2.104(2) Å is shorter than in [Ph3CHP(OSnCl2)Ph2] (2.12(1) Å),19 in the tin(IV) compound [Me3Sn(OPPh3)2][(MeSO2)2N] (2.2261(2) Å),20 and in a triphenylphosphane oxide adduct of a stannylene platinum complex (2.270(4) Å)21 described by Hahn. The Sn(1)−O(1)/ O(2), Sn(1)−Cr(1), and Sn(1)−C(1) distances in 4 and 5 are very similar to those in compounds 2·C7H8 and 3·0.5C7H8. The same holds for the O(1)−Sn(1)−O(2) angles of 150.6(1)° (4) and 156.5(1)° (5). Notably, compound 5 shows the biggest (158.6(1)°) and compound 4 the smallest (137.2(1)°) C(1)− Sn(1)−Cr(1) angle among the compounds 1−5. The 31P NMR spectrum in C6D6 of compound 4 showed a sharp singlet at δ 29.6 (J(31P−117/119Sn) = 141 Hz). Similarly, the spectrum of a solution of compound 3 to which had been added DMAP showed a single resonance at δ 29.7 with J(31P−117/119Sn) of 136/143 Hz, indicating formation of the complex 3·DMAP, which, however, was not isolated. The 119Sn NMR spectrum in C6D6 of compound 4 revealed a triplet resonance at δ 115 (J(119Sn−31P) = 143 Hz). The smaller J(119Sn−31P) coupling constant as compared to the parent compound 2 (see above) reflects the lower electrophilicity of the tin atom in compound 4. Like compound 2, the 1H NMR spectrum showed broad overlapping signals. IR and ESI-MS indicated the presence of DMAP and the perchlorate anion. ESI-MS showed also the typical mass cluster at m/z 773

belonging to RSnCr(CO)5+. The 119Sn NMR spectrum in CD2Cl2 of compound 5 showed an unresolved resonance at δ 67. The 31P NMR spectrum in CD2Cl2 of compound 5 showed a sharp resonance at δ 28.9 [J(31P−117/119Sn) = 182 Hz), signal a] and a broad one at δ 46.4 (ν1/2 = 80 Hz, signal b) with an integral ratio of 2:1. The sharp resonance is assigned to the phosphonyl phosphorus atoms and the broad one to the triphenylphosphane oxide phosphorus atom. At T = 198 K the signal b sharpened (δ 47.2) and showed a J(31P−117/119Sn) = 255 Hz. The 1H NMR spectrum at room temperature showed one signal for the CH isopropyl protons. At T = 189 K and in analogy with the chlorido-substituted compound 1,14d decoalescence into two signals was observed. The data indicate, on the 31P NMR time scale, the kinetic lability of the Ph3P O→Sn coordination in compound 5 at room temperature but kinetic inertness at low temperature. Such temperaturedependent behavior of PO→Sn coordination was also reported for hexamethylphosphoric acid amide, (Me2N)3PO, and related complexes of organotin halides.22 A 31P NMR spectrum in C6D6 of compound 2 to which had been added an excess of the soft Lewis base triphenylphosphane, PPh3, showed resonances at δ 31.0 (2) and −4.4 (PPh3). A 31P NMR spectrum of compound 2 in CD3CN showed a singlet resonance at δ 31.4 (J(31P−117/119Sn = 186/ 195 Hz). The spectrum of this solution to which had been added approximately 0.5 molar equiv of PPh3 showed a slightly broadened singlet resonance c at δ 29.7 (ν1/2 30 Hz) with unresolved J(31P−117/119Sn) satellites of 174 Hz and a broad resonance d at δ 1.8 (ν1/2 100 Hz) belonging to PPh3. Addition of excess PPh3 caused a low-frequency shift of the singlet 2410


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Figure 5. Natural bond orbitals for the nitrogen lone pair at the pyridine ligand resulting in a large charge transfer to the Sn atom (a), the Sn−C σbond (b), and the Sn−Cr σ-bond (c). In (c) also a small contribution of an empty p-orbital at the N-donor atom is observed, resulting in a small charge transfer back to the pyridine ligand.

natural bond orbital is occupied by 1.71e−. The Sn−Cr bond exhibits σ-bond character with main contributions from an sorbital at Sn and dz2,s,pz orbitals at Cr (Figure 5c). In the Sn−C bond the main contribution comes from s- and p-orbitals at Sn and, strangely enough, a nearly C-sp3 hybrid orbital, and thus the interaction can be also assigned as a σ-bond. This picture does not change significantly in the cations of compounds 4 and 5. For the bonding of the tin atom to the 4dimethylaminopyridine ligand no σ-bond is found within the limits of the NBO program. However, a strong donor−acceptor interaction (72 kcal/mol) between the pyridine nitrogen lone pair in the ring plane and the σ* Rydberg orbital at the tin atom was found in compound 4, indicating a more ionic bond from the pyridine ligand to the tin atom. A small back-bonding contribution of the Sn−Cr bond into the localized pz* lone pair of the pyridine nitrogen donor atom results in charge transfer from the tin fragment to the 4-dimethylaminopyridine ligand. In compound 5 a medium strong donor−acceptor interaction (24 kcal/mol) between the tin atom and the O atom of the triphenylphosphane oxide donor ligand was found, indicating the Ph3PO→Sn interaction in 5 to be weaker than the N→ Sn interaction in 4. In all compounds no bonding orbitals between the tin atom and the (i-PrO)2PO oxygen donor atoms of the pincer-type ligand were found. The (i-PrO)2PO→Sn interaction was found to be of donor (oxygen lone pair) to acceptor (Sn s, p) character within the NBO framework with an energy of about 18 kcal/mol. Furthermore, the calculation revealed a slightly increased positive charge at the tin atom in compounds 2 (+1.97) and 5 (+2.01) as compared to compound 4 (+1.86). Comparing the coordinated DMAP ligand in 4 with the noncoordinated DMAP ligand, the charge calculated for the nitrogen donor atom is decreased by 0.13e−, indicating a charge transfer from

resonance c to δ 27.4 accompanied with sharpening and decrease of the (J(31P−117/119Sn) coupling constant to 146/153 Hz. Signal d is also low-frequency shifted to δ −3.6 (ν1/2 100 Hz). Apparently, in a solution of 2 in nonpolar C6D6, PPh3 is not able to replace the perchlorate anion from the coordination sphere of the tin atom to give [4-t-Bu-2,6-{P(O)(OiPr)2}2C6H2(PPh3)SnCr(CO)5][ClO4], 2·PPh3. However, in a solution of the more polar CD3CN, there is an equilibrium between 2 + PPh3 and 2·PPh3 that shifts in favor of the latter on increasing the concentration of PPh3. So far, attempts at isolating 2·PPh3 as analytically pure material failed. DFT Calculations. Geometry optimization (see Computational Details) of the organotin perchlorate complex 2 and the salt-like DMAP- and triphenylphosphane oxide-containing compounds 4 and 5, respectively, revealed geometrical parameters, listed in Table 1, that are in good agreement with the experimental data. However, the Sn−O, Sn−C, and Sn−Cr distances are somewhat longer (ca. 5 pm) than those experimentally obtained. For compound 4, the major difference between the calculated and the experimental structure is a rotation of the dimethylaminopyridine ligand about the Sn−N axis of approximately 90° (Supporting Information, Figure S1). The absence of intermolecular nonbonding interactions in the gas phase structure might be the reason for this difference. For compound 5 a slightly larger bent structure with a Cr−Sn−C angle of 141.5° was calculated, which could also be the result of a lack of intermolecular nonbonding interactions in the calculated structure. To reveal information on bonding and charge transfer in these complexes, NBO analyses were performed.30 In the organotin perchlorate complex 2 the pincer-type ligand is bonded via a Sn−C bond with a natural bond orbital occupied by about 1.90e− which indicates this bond to be covalent. The same holds for the Sn−Cr bond, for which the 2411


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DMAP to the tin atom, compensating part of the positive charge in the cation and thus stabilizing the latter. The charge calculated for the dimethylamino-nitrogen atom does not alter significantly upon coordination to the Sn atom. Also, within the NBO framework no significant π-bond contribution for the N− C bond of the Me2N substituent to the pyridine ring was found. Thus, we conclude that the left resonance structure in Scheme 2 dominates for the description of 4. The higher charge found

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EXPERIMENTAL SECTION

General Procedures. All reactions were carried out under an atmosphere of dry argon in flame-dried glassware using Schlenk techniques. The solvents were purified by distillation from appropriate drying agents under argon. [4-t-Bu-2,6-{P(O)(Oi-Pr)2}2C6H2(Cl)SnCr(CO)5] was synthesized as described.14d Reactions with silver salts were protected from light. NMR spectra were recorded on a Bruker DPX 300/DRX 400/DRX 500 or Varian Mercury instrument at room temperature unless otherwise stated. NMR chemical shifts are given in ppm and were referenced to Me4Si using residual solvent signal (1H, 13C), H3PO4 (85%, 31P), Me4Sn (119Sn), and CCl3F (19F). IR spectra (cm−1) were recorded on a Bruker IFS 28, Bruker 113v, or Perkin-Elmer Spectrum Two spectrometer. Elemental analyses were performed on a LECOCHNS-932 analyzer. Melting points are uncorrected and were measured on a Büchi SMP-20. The electrospray mass spectra were recorded with a Thermoquest-Finnigan instrument using CH3CN as the mobile phase with a concentration of 0.1 mg/mL and a flow rate of 10 μL/min. The experimental isotopic pattern matched the theoretical ones. Warning! Although no problems were encountered in the course of our studies, perchlorate salts are potentially explosive. {[2,6-Bis(diisopropoxyphosphonyl)-4-tert-butyl]phenyl}tin Perchlorate Chromium Pentacarbonyl, [4-t-Bu-2,6-{P(O)(OiPr)2}2C6H2(ClO4)SnCr(CO)5] (2·C7H8). To a solution of [4-t-Bu-2,6{P(O)(O-i-Pr)2}2C6H2(Cl)SnCr(CO)5] (1) (151 mg, 0.19 mmol) in toluene (20 mL) was added silver perchlorate (42 mg, 0.20 mmol). After the suspension had been stirred for 2 d it was filtered, and the filtrate was concentrated in vacuo to a volume of 5 mL. Storing this solution at −30 °C gave compound 2·C7H8 as light green crystals: yield 111 mg, 67%; mp >160 °C (dec); 1H NMR (toluene-d8, 400.13 MHz) δ 0.99 (s, 21H, C(CH3)3 + CH(CH3)2, ν1/2 = 15 Hz), 1.20 (s, 12H, CH(CH3)2, ν1/2 = 20 Hz), 4.81 (s, 4H, CH(CH3)2, ν1/2 = 50 Hz), 7.97 (d, CHaryl, 3J(31P−1H) = 14.0 Hz); 13C{1H} NMR (toluened8, 100.63 MHz) δ 23.0 (s, CH(CH3)2), 23.3 (s, CH(CH3)2), 30.2 (s, C(CH3)3), 34.6 (s, C(CH3)3), 74.6 (s, CH(CH3)2, ν1/2 = 20 Hz), 131.8 (dd, C3/5aryl, 2J(13C−31P) = 13.6 Hz, 4J(13C−31P) = 4.4 Hz), 131.9 (dd, C2/6aryl, 1J(13C−31P) = 189 Hz, 3J(13C−31P) = 19.1 Hz), 154.5 (t, C4aryl, 3J(13C−31P) = 13.0 Hz), 170.4 (t, C1aryl, 2J(13C−31P) = 23.4 Hz), 217.6 (s, COcis), 223.9 (s, COtrans); 31P{1H} NMR (C6D6, 161.98 MHz) δ 31.0 (J(31P−117/119Sn) = 185/194 Hz); 31P{1H} NMR (CD3CN, 121.49 MHz) δ 31.4 (J(31P−117/119Sn = 186/195 Hz); 119 Sn{1H} NMR (C6D6, 111.92 MHz) δ 81 (J(31P−119/117Sn) = 194 Hz); 1H NMR (toluene-d8, 400.13 MHz, 0 °C) δ 0.97 (s, 9H, C(CH3)3), 1.00 (s, 12H, CH(CH3)2, ν1/2 = 22 Hz), 1.20 (s, 6H, CH(CH3)2, ν1/2 = 31 Hz), 4.70 (s, 2H, CH(CH3)2, ν1/2 = 149 Hz), 4.92 (s, 2H, CH(CH3)2, ν1/2 = 150 Hz), 7.98 (d, 2H, CHaryl, 3 31 J( P−1H) = 14.0 Hz); 31P{1H} NMR (toluene-d8, 161.98 MHz, 0 °C) δ 31.0 (J(31P−119/117Sn) = 183 Hz); 1H NMR (toluene-d8, 400.13 MHz, −20 °C) δ 0.94 (s, 9H, C(CH3)3, ν1/2 = 7 Hz), 0.96 (s, 12H, CH(CH3)2, ν1/2 = 39 Hz), 1.15 (s, 6H, CH(CH3)2, ν1/2 = 60 Hz), 1.22 (s, 6H, CH(CH3)2, ν1/2 = 71 Hz), 4.62 (s, 2H, CH(CH3)2 ν1/2 = 42 Hz), 4.93 (s, 2H, CH(CH3)2 ν1/2 = 49 Hz), 7.99 (d, CHaryl, 3 31 J( P−1H) = 13.3 Hz); 31P{1H} NMR (toluene-d8, 161.98 MHz, −20 °C) δ 31.2 (J(31P−119/117Sn) = 191 Hz); 1H NMR (toluene-d8, 400.13 MHz, −30 °C) δ 0.93 (s, 9H, C(CH3)3, ν1/2 = 6 Hz), 0.98 (s, 12H, CH(CH3)2, ν1/2 = 45 Hz), 1.13 (s, 6H, CH(CH3)2, ν1/2 = 31 Hz), 1.24 (s, 6H, CH(CH3)2, ν1/2 = 35 Hz), 4.60 (s, 2H, CH(CH3)2, ν1/2 = 33 Hz), 4.93 (s, 2H, CH(CH3)2, ν1/2 = 35 Hz), 7.99 (d, 2H, CHaryl, 3 31 J( P−1H) = 13.3 Hz); 31P{1H} NMR (toluene-d8, 161.98 MHz, −30 °C) δ 31.3 (J(31P−119/117Sn) = 196 Hz); IR (Nujol) ν̃ = 1179 cm−1 (PO), 1158 cm−1 (PO), 1940 cm−1 (CO), 2058 cm−1 (CO); ESI-MS (positive mode) m/z = 814 [M − ClO4− + CH3CN]+, 773 [M − ClO4−]+, 717 [M − ClO4− − 2 CO]+, 622 [M − ClO4− − Cr(CO)5 + CH3CN]+, 581 [M − ClO4− − Cr(CO)5]+ (100%). Anal. Calcd for C27H39ClO15P2SnCr (871.7): C, 37.2; H, 4.5. Found: C, 37.65; H, 4.5. The analysis was performed with a sample that had been kept at high vacuum in order to remove the toluene solvate.

Scheme 2. Resonance Forms for Compound 4 Illustrating the Delocalization of the Positive Charge

at the tin atom in compounds 2 and 5 is in accord with the small O-donor to tin-acceptor interaction in these compounds. To reveal the nature of the donor−acceptor interaction, the charge transfer in a putative model complex was calculated where the triphenylphosphane oxide was replaced by a triphenylphosphane donor ligand. Recently, Burford and coworkers succeeded in isolating stannylphosphonium ions.23 The NPA charge of +1.73 calculated for the tin atom in the geometry-optimized structure of the triphenylphosphanestabilized cation (see Supporting Information) is smaller than in the DMAP complex 4 (+1.86). In the former compound a covalent bond with an occupation of 1.89e− was found between the tin atom and the phosphane donor atom. In summary our calculations revealed that the donor ligands dimethylaminopyridine and triphenylphosphane decrease the charge at the tin atom to a much stronger extent than O-donor ligands, such as the perchlorate anion and triphenylphosphane oxide ligand, do.

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CONCLUSION From the results presented in this work it is evident that the two strongly coordinating PO-donor functions in the heteroleptic intramolecularly coordinating organostannylene chromium pentacarbonyl complexes [4-t-Bu-2,6-{P(O)(OiPr)2}2C6H2(X)SnCr(CO)5] (X = Cl, ClO4, OTf) are not sufficient to cause, in the solid state, self-ionization under formation of the cation [4-t-Bu-2,6-{P(O)(OiPr)2}2C6H2SnCr(CO)5]+ and the corresponding anions. Only the addition of a third strong donor ligand such as pdimethylaminopyridine or triphenylphosphane oxide stabilizes the cation in the case of perchlorate anion as a leaving group. In the case of compound 4, the stabilization is accomplished by strong transfer of electron density from the pyridine nitrogen to the tin atom but also by some back-donation of electron density from the tin atom into the vacant p*-orbital of the nitrogen atom. DFT calculations suggest the weak Lewis base triphenylphosphane, PPh3, is also capable of stabilizing the cation, but so far, attempts at isolating the corresponding salt [4-t-Bu-2,6-{P(O)(Oi-Pr)2}2C6H2(PPh3)SnCr(CO)5][ClO4] failed, though its existence in solution of polar CD3CN has been proven by 31P NMR spectroscopy. 2412


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Caryl), 132.5 (dd, 1J(13C−31P) = 186.1 Hz, 3J(13C−31P) = 19.0 Hz, C2/6aryl), 133.9 (dd, 2J(13C−31P) = 14.1 Hz, 4J(13C−31P) = 4.4 Hz, C3/5aryl), 145.8 (s, C2pyridine), 156.7 (s, C1pyridine), 157.0 (t, 3J(13C−31P) = 12.1 Hz, C4aryl), 167.6 (t, 2J(13C−31P) = 22.4 Hz, C1aryl), 219.7 (s, 2 13 J( C−117/119Sn) = 118.6 Hz, COcis), 224.9 (s, COtrans); 119Sn{1H} NMR (C6D6, 111.92 MHz) δ 115 (t, J(31P−119Sn) = 143 Hz); 31 1 P{ H} NMR (C6D6, 121.49 MHz) δ 29.6 (s, J(31P−119/117Sn) = 141 Hz); IR (KBr) ν̃ = 2979 cm−1 (CH), 1884−1965 cm−1 (CO), 2054 cm−1 (CO), 1626 cm−1 (DMAP), 1221 cm−1 (ClO4−), 1180 cm−1 (PO), 1092 cm−1 (ClO4−); ESI-MS (positive mode) m/z = 814 [M − DMAP − ClO4− + CH3CN]+, 773 [M − DMAP − ClO4−]+, 717 [M − DMAP − ClO4− − 2 CO]+, 622 [M − DMAP − ClO4− − Cr(CO)5 + CH3CN]+, 581 [M − DMAP − ClO4− − Cr(CO)5]+, 123 [DMAP + H]+ (100%); ESI-MS (negative mode) m/z = 99 [ClO4]−. Anal. Calcd for C34H49ClO15N2P2SnCr (993.9): C, 41.1; H, 5.0; N, 2.8. Found: C, 40.85; H, 5.15; N, 2.65. {[2,6-Bis(diisopropoxyphosphonyl)-4-tert-butyl]phenyl}tin Triphenylphosphane Oxide Perchlorate Chromium Pentacarbonyl, [4-t-Bu-2,6-{P(O)(Oi-Pr)2}2C6H2(Ph3PO)SnCr(CO)5][ClO4] (5). Triphenylphosphane oxide (24 mg, 0.09 mmol) was added to a solution of [4-t-Bu-2,6-{P(O)(O-i-Pr)2}2C6H2(ClO4)SnCr(CO)5] (2) (75 mg, 0.09 mmol) in toluene (3 mL). After the reaction mixture had been stirred for 5 min it was kept for 10 min untouched, during which crystals separated. The crystals were isolated by filtration, washed twice with small amounts of toluene, and dried in vacuo. Yield: 69 mg, 70%; mp 160 °C (dec); 1H NMR (C6D6, 400.13 MHz) δ 1.05−1.15 (not resolved, 24H, CH(CH3)2), 1.17 (s, 9H, C(CH3)3), 4.76−4.85 (not resolved, 4H, CH(CH3)2), 7.01−7.14 (not resolved, 9H, Ph3PO), 7.65−7.69 (not resolved, 6H, Ph3PO), 8.13 (pseudo-d, 3J(31P−1H) = 14.1 Hz, 2H, CHaryl); 13C{1H} NMR (CD2Cl2, 125.76 MHz) δ 23.8− 23.9 (not resolved, CH(CH3)2), 24.0−24.2 (not resolved, CH(CH3)2), 31.4 (s, C(CH3)3), 36.1 (s, C(CH3)3), 75.5−75.6 (not resolved, CH(CH3)2), 126.9 (d, 1J(13C−31P) = 198 Hz, C1 PPh3O), 130.0 (d, J(13C−31P) = 13.4 Hz, C PPh3O), 132.1 (dd, 1J(13C−31P) = 190 Hz, 3J(13C−31P) = 19.2 Hz, C2/6aryl), 132.9 (d, J(13C−31P) = 11.5 Hz, C PPh3O), 133.2 (dd, 2J(13C−31P) = 13.4 Hz, 4J(13C−31P) = 4.8 Hz, C3/5aryl), 134.9 (d, 4J(13C−31P) = 1.9 Hz, C4 PPh3O), 156.6 (t, 3 13 J( C−31P) = 12.2 Hz, C4aryl), 170.2 (C1aryl found in HMBC), 218.3 (s, COcis), 224.0 (s, COtrans); 119Sn{1H} NMR (C6D6, 111.92 MHz) δ 71 (not resolved); 119Sn{1H} NMR (CD2Cl2, 111.92 MHz) δ 67 (not resolved); 31 P{ 1 H} NMR (C 6 D 6 , 121.49 MHz) δ 30.8 (s, J(31P−119/117Sn) = 180 Hz), 36.1 (ν1/2 = 245 Hz); 31P{1H} NMR (CD2Cl2, 121.49 MHz) δ 28.9 (s, J(31P−119/117Sn) = 182 Hz), 46.4 (ν1/2 = 80 Hz); 31P{1H} NMR (CD2Cl2, 121.49 MHz, −34 °C) δ 29.3 (s, J(31P−119/117Sn) = 180 Hz), 47.0 (bs, ν1/2 = 55 Hz); 31P{1H} NMR (CD2Cl2, 121.49 MHz, −75 °C) δ 29.6 (s, J(31P−119/117Sn) = 187 Hz), 47.2 (s, 2J(31P−119/117Sn) = 255 Hz, ν1/2 = 8 Hz); 1H NMR (CD2Cl2, 300.13 MHz, −84 °C) δ 0.55 (not resolved, 6H, CH(CH3)2), 0.91 (not resolved, 6H, CH(CH3)2), 1.17 (not resolved, 6H, CH(CH3)2), 1.32−1.38 (not resolved, 15H, CH(CH3)2 + C(CH3)3), 4.14 (not resolved, 2H, CH(CH3)2), 4.64 (not resolved, 2H, CH(CH3)2), 7.20− 7.75 (not resolved, 15H, Ph3PO), 8.02 (pseudo-d, 3J(31P−1H) = 12.4 Hz, 2H, CHaryl); IR (ATR) ν̃ = 2979 cm−1 (CH), 2058 cm−1 (CO), 1980 cm−1 (CO), 1934 cm−1 (CO), 1906 cm−1 (CO), 1173 cm−1 (PO), 1159 cm−1 (PO), 1134 cm−1 (PO, [Ph3PO]); ESI-MS (positive mode) m/z = 1051 [M − ClO4−]+, 814 [M − Ph3PO − ClO4− + CH3CN]+, 773 [M − Ph3PO − ClO4−]+, 717 [M − Ph3PO − ClO4− − 2 CO]+, 581 [M − Ph3PO − ClO4− − Cr(CO)5]+, 557 [2 Ph3PO + H]+, 279 [Ph3PO + H]+ (100%); ESI-MS (negative mode) m/z = 99 [ClO4−]. Anal. Calcd for C45H54ClO16P3SnCr (1150.0): C, 47.0; H, 4.7. Found: C, 46.6; H, 4.95. Reaction of Compound 2 with PPh3 (NMR Experiment). Triphenylphosphane was added to a solution of [4-t-Bu-2,6-{P(O)(Oi-Pr)2}2C6H2(ClO4)SnCr(CO)5] (2) in C6D6 and CD3CN, respectively. 31P{1H} NMR (C6D6, 121.49 MHz, PPh3:2 = 1:1) δ −4.4 (s, PPh3), 31.0 (s, J(31P−119/117Sn) = 192/184 Hz, 2). 31P{1H} NMR (CD3CN, 121.49 MHz, PPh3:2 = 0.5:1) δ 1.8 (s, ν1/2 = 100 Hz, PPh3), 29.7 (s, ν1/2 = 30 Hz, J(31P−119/117Sn) = 174 Hz). 31P{1H} NMR (CD3CN, 121.49 MHz, PPh3:2 = 5:1) δ −3.6 (s, ν1/2 = 100 Hz, PPh3), 27.4 (s, J(31P−119/117Sn) = 153/146 Hz).

{[2,6-Bis(diisopropoxyphosphonyl)-4-tert-butyl]phenyl}tin Triflate Chromium Pentacarbonyl, [4-t-Bu-2,6-{P(O)(OiPr)2}2C6H2(OTf)SnCr(CO)5] (3·0.5C7H8). To a solution of [4-t-Bu2,6-{P(O)(O-i-Pr)2}2C6H2(Cl)SnCr(CO)5] (1) (200 mg, 0.25 mmol) in toluene (20 mL) was added silver triflate (72 mg, 0.28 mmol). After the reaction mixture had been stirred for 2 h, the suspension was filtered and the filtrate was reduced to a volume of 6 mL. Storing of this solution at −30 °C provided 147 mg (61%) of 3·0.5C7H8 as colorless crystals, mp 180 °C (dec); 1H NMR (400.13 MHz, toluened8) δ 1.01 (s, 21H, C(CH3)3 + CH(CH3)2, ν1/2 = 33 Hz), 1.19 (s, 6H, CH(CH3)2, ν1/2 = 25 Hz), 1.25 (s, 6H, CH(CH3)2, ν1/2 = 25 Hz), 4.69 (s, 2H, CH(CH3)2, ν1/2 = 30 Hz), 4.95 (s, 2H, CH(CH3)2, ν1/2 = 30 Hz), 7.98 (d, 2H, CHaryl, 3J(31P−1H) = 14.3 Hz); 13C{1H} NMR (100.63 MHz, toluene-d8) δ 23.0 (s, ν1/2 = 24 Hz, CH(CH3)2), 23.3 (s, ν1/2 = 14 Hz, CH(CH3)2), 30.2 (s, C(CH3)3), 34.6 (s, C(CH3)3), 74.3−74.7 (complex pattern, CH(CH3)2), 119.8 (q, CF3, 1J(13C−19F) = 318.5 Hz), 131.9 (dd, C3/5aryl, 2J(13C−31P) = 13.6 Hz, 4J(13C−31P) = 4.6 Hz), 131.9 (dd, C2/6aryl, 1J(13C−31P) = 189.0 Hz, 3J(13C−31P) = 19.4 Hz), 154.6 (t, C4aryl, 3J(13C−31P) = 12.1 Hz), 170.6 (t, C1aryl, 2 13 J( C−31P) = 23.6 Hz), 217.6 (s, COcis, 2J(13C−119Sn) = 123.9 Hz), 224.0 (s, COtrans); 31P{1H} NMR (161.98 MHz, toluene-d8) δ 30.2 (J(31P−117/119Sn) = 189 Hz); 119Sn{1H} NMR (149.21 MHz, toluened8) δ 71 (J(31P−119/117Sn) = 193 Hz); 1H NMR (400.13 MHz, toluene-d8, 0 °C) δ 0.98 (s, 15H, C(CH3)3 + CH(CH3)2, ν1/2 = 20 Hz), 1.03 (s, 6H CH(CH3)2, ν1/2 = 43 Hz), 1.17 (s, 6H, CH(CH3)2, ν1/2 = 21 Hz), 1.25 (s, 6H, CH(CH3)2, ν1/2 = 24 Hz), 4.67 (s, 2H, CH(CH3)2, ν1/2 = 29 Hz), 4.93 (s, 2H, CH(CH3)2, ν1/2 = 28 Hz), 7.99 (d, CHaryl, 3J(31P−1H) = 14.3 Hz); 31P{1H} NMR (161.98 MHz, toluene-d8, 0 °C) δ 30.4 (J(31P−119/117Sn) = 189.4 Hz); 1H NMR (400.13 MHz, toluene-d8, −20 °C) δ 0.94 (s, 15H, C(CH3)3 + CH(CH3)2, ν1/2 = 10 Hz), 1.03 (s, 6H, CH(CH3)2, ν1/2 = 15 Hz), 1.15 (s, 6H, CH(CH3)2, ν1/2 = 14 Hz), 1.25 (s, 6H, CH(CH3)2, ν1/2 = 15 Hz), 4.65 (s, 2H, CH(CH3)2, ν1/2 = 25 Hz), 4.92 (s, 2H, CH(CH3)2, ν1/2 = 25 Hz), 8.00 (d, 2H, CHaryl, 3J(31P−1H) = 14.1 Hz); 31P{1H} NMR (161.98 MHz, toluene-d8, −20 °C) δ 30.6 (J(31P−119/117Sn) = 185 Hz); 1H NMR (400.13 MHz, toluene-d8, −40 °C) δ 0.92 (s + d, 15H, C(CH3)3 + CH(CH3)2, ν1/2 = 14 Hz), 1.03 (d, 6H CH(CH3)2, 3 1 J( H−1H) = 5.5 Hz), 1.15 (d, 6H, CH(CH3)2, 3J(1H−1H) = 5.8 Hz), 1.26 (d, 6H, CH(CH3)2, 3J(1H−1H) = 5.5 Hz), 4.62−4.66 (complex pattern, 2H, CH(CH 3 ) 2 ), 4.87−4.90 (complex pattern, 2H, CH(CH3)2), 8.01 (d, 2H, CHaryl, 3J(31P−1H) = 14.1 Hz); 31P{1H} NMR (161.98 MHz, toluene-d8, −40 °C) δ 30.8 (J(31P−119/117Sn) = 185 Hz); 1H NMR (400.13 MHz, toluene-d8, −70 °C) δ 0.88 (s + d, 15H, C(CH3)3 + CH(CH3)2, ν1/2 = 19 Hz), 1.03 (d, 6H, CH(CH3)2, 3 1 J( H−1H) = 5.8 Hz), 1.15 (d, 6H, CH(CH3)2, 3J(1H−1H) = 5.8 Hz), 1.27 (d, 6H, CH(CH3)2, 3J(1H−1H) = 5.5 Hz), 4.58−4.65 (complex pattern, 2H, CH(CH 3 ) 2 ), 4.80−4.88 (complex pattern, 2H, CH(CH3)2), 8.04 (d, 2H, CHaryl, 3J(31P−1H) = 14.1 Hz); 31P{1H} NMR (161.98 MHz, toluene-d8, −70 °C) δ 31.3 (J(31P−119/117Sn) = 185 Hz); IR (Nujol) ν̃ = 1179 cm−1 (PO), 1939 cm−1 (CO), 2058 cm−1 (CO). Anal. Calcd for C28H39P2O14SSnF3Cr·0.5C7H8 (967.35): C, 39.1; H, 4.5. Found: C, 38.5; H, 4.6. {[2,6-Bis(diisopropoxyphosphonyl)-4-tert-butyl]phenyl}tin 4-(dimethylamino)pyridine Perchlorate Chromium Pentacarbonyl, [4-t-Bu-2,6-{P(O)(Oi-Pr) 2 } 2 C 6 H 2 (4-Me 2 NC 5 H 4 N)SnCr(CO)5][ClO4] (4). 4-(Dimethylamino)pyridine (109 mg, 0.89 mmol) was added to a solution of [4-t-Bu-2,6-{P(O)(Oi-Pr)2}2C6H2(ClO4)SnCr(CO)5]·C7H8 (2·C7H8) (856 mg, 0.89 mmol) in toluene (30 mL). After stirring overnight the solution was filtered over Celite and concentrated in vacuo to a volume of ca. 10 mL. Colorless crystals were obtained after one day. The crystals were washed with a little toluene and dried in vacuo. Yield: 640 mg, 56%; mp 153 °C (dec); 1H NMR (C6D6, 400.13 MHz) δ 1.02−1.10 (not resolved, 12H, CH(CH3)2), 1.12 (d, 3J(1H−1H) = 6.1 Hz, 6H, CH(CH3)2), 1.32 (s, 9H, C(CH3)3), 1.38−1.53 (not resolved, 6H, CH(CH3)2,), 2.40 (s, 6H, N(CH3)2), 4.51−4.81 (not resolved, 4H, CH(CH3)2), 6.55−6.75 (not resolved, 2H, Hpyridine), 8.10−8.29 (not resolved, 4H, CHaryl + Hpyrdine); 13 C{1H} NMR (C6D6, 100.63 MHz) δ 23.8−24.6 (not resolved, CH(CH3)2), 31.2 (s, C(CH3)3), 35.9 (s, C(CH3)3), 39.3 (s, N(CH3)2), 75.3−76.5 (not resolved, CH(CH3)2), 109.0 (s, C3pyridine), 127.4 (s, 2413


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Reaction of Compound 3 with DMAP (NMR Experiment). DMAP was added to a solution of 4-t-Bu-2,6-{P(O)(OiPr)2}2C6H2(OTf)SnCr(CO)5] (3) in C6D6. 31P{1H} NMR (C6D6, 121.49 MHz) δ 29.7 (s, J(31P−117/119Sn) = 136/143 Hz). Reaction of Compound 1 with DMAP (NMR Experiment). Compound 1 was dissolved in C6D6 and CD3CN, respectively. 31 1 P{ H} NMR (C6D6, 81.02 MHz) δ 30.6 (s, J(31P−117/119Sn) = 175/ 183 Hz); 31P{1H} NMR (CD3CN, 81.02 MHz) δ 30.1 (s, J(31P−117/119Sn) = 172/180 Hz). To these solutions DMAP (excess) was added. 31 P{ 1 H} NMR (C 6D 6, 81.02 MHz) δ 30.6 (s, J(31P−117/119Sn) = 175/183 Hz); 31P{1H} NMR (CD3CN, 81.02 MHz) δ 30.1 (s, J(31P−117/119Sn) = 172/180 Hz). Crystallography. Intensity data for the crystals 2·C7H8 and 3·0.5C7H8 were collected on a Nonius KappaCCD diffractometer (Bruker), and for crystals 4 and 5 on an Xcalibur2 CCD diffractometer (Oxford Diffraction), all with graphite-monochromated Mo Kα radiation at 173 K. The structure was solved by direct methods with SHELXS-97.24 Refinements were carried out against F2 by using SHELXL-97.24 The C−H hydrogen atoms were positioned with idealized geometry and refined using a riding model. All non-hydrogen atoms were refined using anisotropic displacement parameters. In 2·C7H8 a disordered perchlorate group was found with five positions of oxygen atoms where one was refined with an occupancy of 1 and four with occupancies of 0.75. One isopropoxy group is disordered over two sites with occupancies of 0.5 (C(23), C(23′). In compound 3·0.5C7H8 the triflate anion (except O(3) and S(1)) is affected by disorder and refined by a split model. The two sites are occupied in a 0.6 to 0.4 ratio and restrained to nearly isotropic behavior. Three oxygen atoms from the perchlorate group of 4 are affected by disorder, occupying two positions in a 0.7 (for O(11), O(12), O(13)) to 0.3 (for O(11′), O(12′), O(13′)) ratio. The carbon atom C(12) is also disordered over two sites, with occupancies of 0.7 for C(12) and 0.3 for C(12′), and restrained to nearly isotropic behavior. In compound 5 the tert-butyl group is disordered over two sites with an occupancy ratio of 0.5 to 0.5. The crystallographic data are given in Tables S1 and S2. CCDC-908663 (2·C7H8), CCDC-908664 (3·0.5C7H8), CCDC908665 (4), and CCDC-908666 (5) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www. ccdc.cam.ac.uk/data_request/cif. Computational Details. For all calculations at the density functional theory level, the program Gaussian09 was used.25 Energies and geometries were developed at the nonlocal level of theory. For geometry optimization the energies were corrected for nonlocal exchange according to Becke26 and for nonlocal correlation according to Perdew (BP-86).27 The def2-TZVP split valence basis set was used for all atoms.28 For Sn we used an effective core potential base set (ECP-46-mwb) with an additional f-function.29 For the analysis of natural charges (NPA) and natural bonds the NBO program version 3.1 was used as implemented in the Gaussian09 program.30 Stationary points, i.e., minima, where checked by second-derivative calculations, revealing no imaginary frequencies.

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AUTHOR INFORMATION

DFT calculations This work contains part of the planned Ph.D. thesis of M. Wagner, TU Dortmund, and of the Ph.D. thesis of M. Henn, TU Dortmund, 2004. Parts of the results presented here were first presented at the XVth FECHEM Conference on Organometallic Chemistry, University of Zürich, August 10− 15, 2003, Book of Abstracts OP38, at the 11th International Conference on the Coordination and Organometallic Chemistry of Germanium, Tin, and Lead (ICCOC-GTL-11), Santa Fe (NM, USA), June 27 to July 2, 2004, Book of Abstracts O54, and at International Symposium on Inorganic Ring Systems (IRIS), July 29−August 2, 2012, Victoria, Canada, Book of Abstracts O53. †

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ACKNOWLEDGMENTS M.W. is grateful to TU Dortmund for a scholarship. We acknowledge anonymous reviewers for their valuable comments. Dedicated to Professor Joachim Heinicke on the occasion of his retirement.

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REFERENCES

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S Supporting Information *

CIF files for compounds 2·C7H8, 3·0.5C7H8, 4, and 5, calculated structures for the cations in 4, 5, and hypothetical [R(Ph 3 P)SnCr(CO) 5 ] + (R = 4-t-Bu-2,6-[P(O)(OiPr)2]2C6H2), and tables containing crystallographic data. This material is available free of charge via the Internet at http:// pubs.acs.org. Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. 2414


Organometallics

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