Article Cite This: Organometallics XXXX, XXX, XXX−XXX
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Metal-Alkyne and Metallacyclobutene Reactivity toward a Diazoacetamide: Conversion to Highly Functionalized 1,3-Diene Complexes and Oxametallacyclopentadienes Pengjin Qin, Ryan L. Holland, Curtis E. Moore, and Joseph M. O’Connor* Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
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ABSTRACT: Here we report the first reactions of metalalkyne and metallacyclobutene complexes with a diazoacetamide. Reaction of (η5-C5H5)(PPh3)Co[η2-(R3Si)CC(SO2Ar)] (1-TMS, R = Me, Ar = C6H5; 1-TIPS, R = CH(CH3)2, Ar = p-C6H4CH3) and 2-diazo-N,N-dimethylacetamide, N2CH(CONMe2) (7), produces the oxametallacyclopentadiene complexes (η5-C5H5)(SO2Ar)Co[κ2-OC(NMe2)CC(H)C(R3Si)] (8-TMS, R = Me, Ar = C6H5; 8-TIPS, R = CH(CH3)2, Ar = p-C6H4CH3). The conversion of 1 and 7 to 8 involves the loss of PPh3, two nitrogen atoms, and a single carbon atom from the starting materials, as well as cleavage of a carbon−sulfur bond and formation of a sulfinato (−SO2Ar) ligand. The cobalt-alkyne complex, (η5C5H5)(PPh3)Co(η2-PhCCPh) (1-Ph), undergoes reaction with 7 to give the cobalt-diene complex (η5-C5H5)Co[η4-(Z,E)CH(CONMe2)CPhCPhCH(CONMe2)] (9-ZE). Treatment of the cobaltacyclobutene, (η5-C5H5)(PPh3)Co[κ2-(3ethoxycarbonyl)-1-(phenylsulfonyl)-2-(trimethylsilyl)-1-propene-1,3-diyl] (3-TMS), with 7 leads to regio- and diastereoselective formation of a highly functionalized cobalt-1,3-diene complex (η5-C5H5)Co[η4-(Z,E)-CH(CONMe2)C(SO2Ph) C(TMS)CH(CO2Et)] (10-ZE). The structures of 8-TMS, 8-TIPS, 9-ZE, and 10-ZE are established by single-crystal X-ray crystallographic analyses.
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INTRODUCTION The regio- and diastereoselective addition of two carbenes across an alkyne is a conceptually elegant route toward highly substituted/functionalized 1,3-dienes (I, Figure 1).1−4 Hong
Scheme 1. Reactions of 1-TMS and 1-TIPS with Ethyl Diazoacetate (2)
Figure 1. Formal addition of two different carbenes across an unsymmetrically substituted alkyne to generate a tetrasubstituted 1,3diene.
and co-workers first reported the formal addition of two carbenes across an alkyne for the reaction of (η5-C5H5)Co(PPh3)(η2-PhCCPh) (1-Ph) with excess ethyl diazoacetate.1 This remarkable transformation was suggested to proceed via the intermediacy of an unsaturated metallacyclobutene (e.g., II). We previously reported the reactions of cobalt-alkyne complexes 1-TMS and 1-TIPS with ethyl diazoacetate (2) to give metallacyclobutenes, 3-TMS and 3-TIPS, respectively (Scheme 1).2a,b Reaction of the metallacycles with additional ethyl diazoacetate produced cobalt-1,3-diene complexes 4-EETMS and 4-EE-TIPS, respectively. In the case of 3-TMS, © XXXX American Chemical Society
diastereomeric diene complexes 4-ZE-TMS and 4-EZ-TMS were also formed. The related reactions of 1-TMS with the diazoketones N2CHCOMe (5-Me) and N2CHCOPh (5-Ph) generated 1,3-(Z,E)-diene complexes 6-ZE-Me and 6-ZE-Ph, respectively, with no spectroscopic evidence for the formation of metallacyclobutenes (eq 1).3 Received: November 14, 2018
A
DOI: 10.1021/acs.organomet.8b00838 Organometallics XXXX, XXX, XXX−XXX
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Organometallics
We have now examined the reactivity of the relatively electron-rich diazocarbonyl, 2-diazo-N,N-dimethylacetamide (7),5,6 toward cobalt-alkyne complexes 1-TMS and 1-TIPS. Unexpectedly, the reactions of 1-TMS and 1-TIPS with 7 generate oxametallacyclopentadiene-sulfinato products (η5C 5 H 5 )(SO 2 Ar)Co[κ 2 -{OC(NMe 2 )CHC(SiR 3 )}] (8TMS, R = Me, Ar = C6H5 and 8-TIPS, R = CH(CH3)2, Ar = p-C6H4CH3), which have been characterized by X-ray crystallography. The diphenylacetylene complex 1-Ph and cobaltacyclobutene 3-TMS undergo reaction with 7 to produce the respective cobalt-(Z,E)-1,3-diene complexes, (η5-C5H5)Co[η4-(ECHCPhCPhCHE)] (9-ZE; E = CONMe2) and (η 5 - C 5 H 5 ) C o { η 4 - [ E C H C ( S O 2 P h ) C ( T M S ) C H (CO2Et)]} (10-ZE; E = CONMe2).7
Figure 2. Spectroscopic data eliminate III−VI as viable structures for 8-TMS and 8-TIPS.
data for 8-TMS indicated the presence of only 19 carbon atoms, thereby ruling out oxametallabenzene structure VI. Ultimately, single-crystal X-ray analyses revealed 8-TMS and 8-TIPS to be oxametallacyclopentadiene-sulfinato complexes (Figure 3, Table 1).9,10 Structurally characterized oxacobalta-
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RESULTS AND DISCUSSION The cobalt-alkyne complexes 1-TMS and 1-TIPS underwent reaction with 2-diazo-N,N-dimethylacetamide (7; 2 equiv) in dry toluene under an inert atmosphere to produce 8-TMS (34% yield) and 8-TIPS (30%), respectively (Scheme 2). The Scheme 2. Reaction of Diazoacetamide 7 with Cobalt Alkyne Complexes 1-TMS and 1-TIPS Generates Oxametallacyclopentadiene Products (8)
Figure 3. ORTEP drawings of 8-TIPS (upper panel) and 8-TMS (lower panel). All hydrogen atoms except H(2) are omitted for clarity.
spectroscopic data suggest very similar structures for the isolated products. In the 1H NMR (CDCl3) spectrum of 8TMS, downfield resonances are observed at δ 7.5−8.1 (m, 5H) and 6.44 (s, 1H), indicating the presence of a phenylsulfonyl group and a vinyl hydrogen. Incorporation of an amido group is supported by two singlets at δ 2.88 (3H, NMe) and 2.91 (3H, NMe), and the presence of a low energy carbonyl IR absorption at 1590 cm−1 (CDCl3). The low energy IR absorption is consistent with coordination of the amide oxygen to cobalt. For comparison, the rhodium oxametallacycle, (PiPr3)2Rh(Cl)(H)[κ2-(CHCHCONH2)], exhibits ν(CO) at 1567 cm−1 (KBr).8 On the basis of the 1H NMR and IR spectroscopic data, it is possible to rule out cobaltacyclobutene (III), η3-vinylcarbene (IV), and cobaltdiene (V) structures for 8-TMS (Figure 2). Unexpectedly, the 13 C{1H} NMR (CDCl3) spectroscopic and mass spectrometry
cyclopentadiene complexes are relatively rare,11 and 8-TMS/8TIPS appear to be the first examples that involve an amide oxygen. The Co−C(1)−C(2)−C(3)−O(1) rings in 8 are nearly planar, with the largest displacements of a ring-atom from the mean plane being O(1) (−0.0350(18) Å) for 8-TMS and C(1) (+0.0274(14) Å) for 8-TIPS. The conformation about the C(3)−N bond places the C(9)−N−C(10) mean plane parallel to the metallacycle ring plane, with a plane− plane dihedral angle of 7.3(2)° for 8-TIPS and 9.2(3)° for 8TMS. In 8-TMS, the 1.348(5) Å C(1)−C(2) distance and 1.469(5) Å C(2)−C(3) distance indicate significant carbon− carbon double bond character at C(1)−C(2). Similar bond metrics are observed for 8-TIPS, with the most notable difference being a more acute Co−C(1)−Si angle in 8-TMS (129.5(2)°) relative to that in 8-TIPS (135.5(2)°). B
DOI: 10.1021/acs.organomet.8b00838 Organometallics XXXX, XXX, XXX−XXX
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Organometallics Table 1. Distances (Å) and Angles (deg) from the X-ray Crystallographic Data for 8-TMS, 8-TIPS and 11 cnt
Co−Cp Co−C(1) Co−S Co−O(1) C(1)−C(2) C(2)−C(3) C(3)−O(1) C(1)−Si C(3)−N Co−O(1)−C(2) C(1)−Co−O(1) Co−C(1)−C(2) C(1)−C(2)−C(3) C(2)−C(3)−O(1) S−Co−C(1) S−Co−O(1)
8-TMS
8-TIPS
11
1.699(2) 1.937(4) 2.190(1) 1.935(2) 1.348(4) 1.457(4) 1.283(3) 1.880(3) 1.328(3) 113.4(2)
1.702(2) 1.954(4) 2.192(1) 1.923(2) 1.346(5) 1.462(5) 1.273(4) 1.914(4) 1.328(4) 113.2(2)
110.6(2) 115.9(2) 115.5(2) 90.6(1) 93.4(1)
109.2(2) 116.2(3) 116.1(3) 89.7(1) 90.5(1)
1.667(1) 1.914(2) − 1.950(2) 1.338(3) 1.434(3) 1.239(3) − − 110.9(2) 84.4(1) 111.0(2) 114.2(3) 119.4(2) − −
at room temperature also led to the formation of 12 in 78% isolated yield. Thus, the missing carbon atom appears to have been converted to CO. The 27% yield of 12 makes it unlikely that the CO oxygen originated from adventitious oxygen or water in the reaction mixture. Furthermore, in solution, the alkyne complexes 1TMS and 1-TIPS decomposed upon exposure to air, and the reaction of 1-TMS with 7 in 18OH2-saturated C6D6 resulted in decomposition of 1-TMS, with no formation of 8-TMS or 12.13An alternative source for the oxygen in byproduct 12 is the sulfone group of an organometallic complex (e.g., 1-TMS), or an organic compound such as TMSCCSO2Ph.14 Scheme 3 provides a mechanism for incorporation of a sulfone oxygen Scheme 3. Mechanistic Speculation for the Conversion of 1TMS and 7 to 8-TMS and 12
The structural data for 8-TIPS indicate a major resonance contribution from charge-separated resonance structure 8TIPS-II, with a relatively minor contribution from metallafuran structure 8-TIPS-III (Figure 4). This contrasts markedly with
into the CO ligand of 12. Attack of the sulfone oxygen at the carbene carbon of VI15 would generate zwitterion VII followed by fragmentation to intermediate VIII and an alkynyl sulfoxide. Subsequent decarbonylation would lead to IX from which CO dissociation produces 8. Reaction of liberated CO with 1-TMS provides a reasonable explanation for the formation of byproduct 12. This mechanism is highly speculative and efforts to increase the yield of 8-TMS by the addition of DMSO or dimethylsulfone were unsuccessful. Reaction of the liberated sulfoxide with other species (e.g., 1-TMS, 7, IV, VI, etc.) may lead to the trace amounts of unidentified byproducts.16 The disparate outcomes observed for the reaction of 1-TMS with diazoacetamide vs diazoester reagents may be a consequence of differences in the relative stabilities and reactivity of the corresponding vinylcarbene intermediates (e.g., IV and VI vs analogues derived from a diazoester). Regardless of the mechanism by which 8 forms, it is clear that the diazo reagent has coupled to a carbon of the alkyne ligand in 1. In an effort to establish the reactivity of 7 toward a complex that is less capable of alkyne fragmentation, we turned to the reaction of 1-Ph and 7. Treatment of a toluene solution of 1-Ph with 5 equiv of 7 at ambient temperature led to formation of the cobalt-diene complex 9-ZE as a single diastereomer in 81% isolated yield (Scheme 4). In the 1H NMR spectrum (CDCl3) of 9-ZE, singlets at δ 1.73 (1H) and 3.54 (1H) are attributed to the anti and syn hydrogens of the
Figure 4. Comparison of resonance contributors for 8 and 11.
the data for literature oxacobaltacycle 11,11b which exhibits a significantly longer Co−O(1) distance and significantly shorter C(3)−O(1) and Co−C(1) distances. Thus, carbene (metallafuran) resonance structure III is a more significant contributor for 11 than for 8. We attribute this difference in the relative resonance contributors for 8 and 11 primarily to the better pi-donor ability of nitrogen relative to oxygen. The mechanism of formation for 8 must be complex. In an effort to determine the fate of the missing carbon atom, a reaction of 1-TMS and 7 in dry, degassed benzene-d6 was monitored by 1H NMR spectroscopy (see Figure S1 and S2). After 16 h at ambient temperature, analysis indicated the expected formation of 8-TMS (38.5%), as well as a 27% yield of a second cyclopentadienyl-cobalt product (δ 4.61, s). Additional resonances attributed to trace amounts of uncharacterized byproducts were observed at δ 4.40, 4.68, 4.71, 4.76, 4.84, 4.88, 5.11, 5.38, and 6.27. Our initial speculation that the δ 4.61 resonance is due to (η5C5H5)(PPh3)Co(CO) (12) was confirmed by comparison of the NMR and IR spectroscopic data to those for an authentic sample of 12 prepared from (η5-C5H5)Co(PPh3)2 (13) and CO (eq 2).12 Notably, treatment of 1-TMS with 1 atm of CO C
DOI: 10.1021/acs.organomet.8b00838 Organometallics XXXX, XXX, XXX−XXX
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Organometallics
reaction with a vinylcarbene derived from 3-TMS to give a 1,3diene bearing four different functional groups. Reaction of 3TMS with 1.5 equiv of 7 proceeded at 70 °C (6 h) to give a 53% yield of 10-ZE (Scheme 5). In the 1H NMR spectrum
Scheme 4. Reaction of Diazoacetamide 7 with CobaltAlkyne Complex 1-Ph
Scheme 5. Reaction of Diazoacetamide 7 with Cobaltacyclobutene 3-TMS
(CDCl3) of 10-ZE, resonances at δ 1.44 (s, 1H, Hanti) and 3.53 (s, 1H, Hsyn) indicate ZE stereochemistry, as was observed for cobalt-diene complexes 6 and 9.17 A single-crystal X-ray analysis confirmed that the amide-substituted carbene had coupled to the metallacyclobutene carbon bearing the sulfone substituent, and that the amide and sulfone groups are syn (Figure 6). This stereochemical outcome is consistent with
diene ligand, respectively. For comparison, the analogous diene complex (η5-C5H5)Co[η4-(Z,E)-CH(CO2Et)CPhCPh CH(CO2Et)], derived from 1-Ph and ethyl diazoacetate, exhibits resonances in CDCl3 at δ 1.70 (s, Hanti) and 3.70 (s, Hsyn).1 The structure of 9-ZE was confirmed by an X-ray crystallographic analysis (Figure 5).
Figure 6. ORTEP drawing of 10-ZE. Selected bond distances (Å): Co−C(1), 2.018(2); Co−C(2), 1.970(2); Co−C(3), 1.994(2); Co− C(4), 2.018(2); C(1)−C(2), 1.449(3); C(2)−C(3), 1.447(3); C(3)−C(4), 1.456(3); C(1)−C(5), 1.485(3); C(5)−O(1), 1.238(2); C(6)−O(2), 1.231(2); O(2)−H(1) 2.152(2). All hydrogen atoms except H(1) and H(4) are omitted for clarity.
Figure 5. ORTEP drawing of 9-ZE. Selected bond distances (Å): Co−C(1), 2.037(2); Co−C(2), 2.010(2); Co−C(3), 2.002(2); Co− C(4), 2.026(2); C(1)−C(2), 1.449(3); C(2)−C(3), 1.434(3); C(3)−C(4), 1.452(3); C(1)−C(5), 1.487(3); C(4)−C(6), 1.495(3); C(5)−O(1), 1.238(2); C(6)−O(2), 1.238(3); O(2)− H(1) 2.156(2). All hydrogen atoms except H(1) and H(4) are omitted for clarity.
that observed from reaction of 3-TMS with diazoketones 5 (eq 1). We propose the intermediacy of a η3-vinylcarbene (XII) for the conversion of 3-TMS to 10-ZE (Scheme 5). Mechanistic possibilities for this conversion include either direct attack of the diazo reagent at the carbene carbon, or initial diazoacetamide attack at cobalt followed by carbon−carbon bond formation, as shown in Scheme 6.
We previously found that 3-TIPS exists in equilibrium with the η3-vinylcarbene complex 13-TIPS (eq 3), and calculations
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CONCLUSION In summary, a surprising carbon-extrusion reaction has been uncovered for the reaction of sulfone-substituted alkyne complexes with a diazoacetamide. The reaction mechanism must be highly complex, involving the cleavage of a carbon− sulfur bond and the loss of a single carbon atom, which appears to be incorporated into the carbon monoxide ligand of the (η5C5H5)Co(PPh3)(CO) byproduct. Notably, the diphenylacety-
indicated that 13-TIPS is more stable than the unsaturated cobaltacyclobutene analogue.2b We therefore propose that 9ZE is formed via the intermediacy of a vinylcarbene intermediate (e.g., X or XI), which undergoes reaction with a second equivalent of 7 (Scheme 4).The above results suggested that 7 may undergo a regio- and stereoselective D
DOI: 10.1021/acs.organomet.8b00838 Organometallics XXXX, XXX, XXX−XXX
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Organometallics
36.5% yield). mp 135.5 °C; IR (CDCl3) 2947, 2892, 1590, 1442, 1417, 1402 cm−1. 1H NMR (400 MHz, CDCl3) δ 0.44 (s, 9H), 2.88 (s, 3H), 2.91 (s, 3H), 5.09 (s, 5H), 6.44 (s, 1H), 7.5−8.1 (m, 5H); 13 C{1H} NMR (500 MHz, CDCl3) δ 1.08, 35.53, 40.13, 87.36, 126.94, 127.13, 129.58, 136.87, 151.23, 177.09, 223.86. HRMS for [C19H26CoNO3SSiNa]+: 458.0627 (Theo. Mass), 458.0626 (Mass Measured), Delta (−0.2 ppm). Elemental Analysis: C% (52.40); H% (6.02). Found: C% (52.20); H% (6.40). (η5-C5H5)(SO2Tol)Co[κ2-OC(NMe2)CHC(SiiPr3)] (8-TIPS; Tol = p-C6H4CH3). A toluene solution (150 mL) of 1-TIPS (460 mg, 0.624 mmol) and 7 (110 mg, 0.972 mmol) was heated at 70 °C for 5 h. Following chromatographic purification (silica gel, 80% ethyl acetate/ hexane) and recrystallization (toluene/hexanes), 8-TIPS (101 mg, 30.3% yield) was obtained as an air-stable, dark crystalline solid. mp 150.2 °C; IR (CDCl3) 2920, 2942, 2861, 1590, 1466, 1421, cm−1. 1H NMR (400 MHz, CDCl3) δ 1.28 (d, 9H, 3JHH = 7.6 Hz), 1.32 (d, 9H, 3 JHH = 7.2 Hz), 1.50 (m, 3H), 2.41 (s, 3H), 3.00 (s, 3H), 3.13 (s, 3H), 4.94 (s, 5H), 6.74 (s, 1H), 7.21 (d, 2H, 3JHH = 8.0 Hz), 7.72 (d, 2H, 3 JHH = 8.0 Hz). 13C{1H} NMR (500 MHz, CDCl3) δ 13.42, 19.58, 19.91, 21.52, 35.57, 40.40, 87.41, 125.67, 128.42, 139.52, 140.52, 153.28, 176.79, 219.26. HRMS for [C26H40CoNO3SSiNa]+: 556.1722 (Theo. Mass), 556.1722 (Mass Measured), Delta (0 ppm). Elemental Analysis: C% (58.51); H% (7.55). Found: C% (58.19); H% (7.94). (η5-C5H5)Co[η4-(E,Z)-CH(CONMe2)CPhCPhCH(CO NMe2)] (9ZE). A toluene solution (50 mL) of the cobalt-alkyne complex, (η5C5H5)(PPh3)Co(η2-PhCCPh) (1-Ph; 200 mg, 0.35 mmol) and N,N-dimethyldiazoacetamide (7; 200 mg, 1.77 mmol) was stirred at ambient temperature for 48 h under inert atmosphere. A chromatographic workup (silica, 25% ethyl acetate/hexanes) and recrystallization (toluene/hexanes) led to the isolation of 9-ZE as an air-stable dark red crystalline solid (136 mg, 81.3% yield). mp 139.2 °C; IR (CDCl3) 3084, 3056, 3022, 2925, 2237, 1624, 1607, 1488, 1421, cm−1. 1H NMR (400 MHz, CDCl3) δ 1.73 (s, 1H), 2.80 (s, 3H), 2.85 (s, 3H), 3.02 (s, 3H), 3.31 (s, 3H), 3.54 (s, 1H), 5.07 (s, 5H), 6.9− 7.4 (m, 10H); 1H NMR (400 MHz, C6D6) δ 2.26 (s, 1H, Hanti), 2.58 (s, 3H), 2.73 (s, 6H), 2.80 (s, 3H), 3.38 (s, 1H, Hsyn), 4.93 (s, 5H), 6.9−7.6 (m, 10H). 13C{1H} NMR (500 MHz, C6D6) δ 35.27, 37.69, 40.08, 47.75, 83.90, 94.75, 104.79, 126.81, 126.95, 127.30, 127.69, 131.44, 132.20, 138.44, 141.70, 171.74, 172.63. HRMS for [C27H30CoN2O2]+: 473.1634 (Theo. Mass), 473.1626 (Mass Measured), Delta (−1.7 ppm). Elemental Analysis: C% (68.64); H % (6.19). Found: C% (68.76); H% (6.51). (η 5 -C 5 H 5 )Co[η 4 -(E,Z)-CH(CO 2 Et)C(TMS)C(SO 2 Ph)CH (CONMe2)] (10-ZE). A toluene solution (100 mL) of cobaltacyclobutene 3-TMS (500 mg, 0.70 mmol) and 7 (120 mg, 1.06 mmol) was heated at 70 °C for 6 h. Following a chromatographic workup (silica gel, 20% ethyl acetate/hexanes) and recrystallization (ethyl acetate/ hexanes), 10-ZE (197 mg, 52.8% yield) was isolated as an air-stable, dark red, crystalline solid. mp 158.8 °C; IR (CDCl3) 3059, 2978, 2951, 2898, 2251, 1677, 1668, 1531, 1481, 1434, cm−1. 1H NMR (400 MHz, CDCl3) δ 0.50 (s, 9H), 1.22 (t, 3H, 3JHH = 7.2 Hz), 1.44 (s, 1H, Hanti), 2.41 (s, 3H), 2.49 (s, 3H), 3.53 (s, 1H, Hsyn), 3.93 (m, 2H), 5.15 (s, 5H), 7.41 (t, 2H, 3JHH = 7.2 Hz), 7.49 (t, 1H, 3JHH = 7.2 Hz), 7.83 (d, 2H, 3JHH = 7.2 Hz). 13C{1H} NMR (500 MHz, CDCl3) δ 2.22, 14.52, 35.72, 37.60, 37.62, 46.63, 60.40, 83.54, 84.86, 113.85, 127.84, 128.45, 132.42, 142.06, 170.52, 173.77. HRMS for [C24H33CoNO5SSi]+: 534.1175 (Theo. Mass), 534.1170 (Mass Measured), Delta (−0.9 ppm). Elemental Analysis: C% (54.02); H % (6.04). Found: C% (53.88); H% (6.11). Preparation of (η5-C5H5)Co(PPh3)(CO) (12). This procedure involves a slight modification of a published procedure. Carbon monoxide was bubbled through a toluene solution (200 mL) of CpCo(PPh3)2 (150 mg; 0.231 mmol) for 5 min, during which time the color of the solution changed from red to orange brown. The volatiles were evaporated in vacuo, and the residue was washed with hexanes to remove triphenylphosphine. The brown residue was filtered and dried under vacuum to afford 12 as a brown air-sensitive solid (75 mg; 78.4% yield). The spectral data matched the literature values.12
Scheme 6. Mechanistic Possibilities for the Conversion of Vinylcarbene Intermediates to Metal-Diene Products
lene complex 1-Ph undergoes reaction with diazoacetamide 7 to give a high yield of cobalt-diene complex 9-ZE, with no evidence for diastereomeric diene isomers. Alternatively, the metallacyclobutene complex 3-TMS undergoes reaction with 7 to give a single diastereomer of the tetra-functionalized 1,3diene complex 10-ZE. The formation of both diene complexes is proposed to involve the reaction of 7 with an unobserved vinylcarbene intermediate.
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EXPERIMENTAL SECTION
General Information. All manipulations were carried out under an atmosphere of dry dinitrogen using standard Schlenk or glovebox techniques. NMR-scale reactions were performed under a dry dinitrogen atmosphere in 5 mm J-Young style NMR tubes equipped with a Teflon needle-valve adapter using freshly degassed solvents (freeze/pump/thaw procedure). Chloroform-d was dried and stored over calcium hydride under a dinitrogen atmosphere. Toluene and hexanes were dried on columns of activated alumina using a J. C. Meyer (formerly Glass Contour) solvent purification system. Flash column chromatographic purifications were performed using silica gel (60 Å, particle size 43−60 μm, 230−400 mesh, EMD Chemicals). Combustion analysis was performed by NuMega laboratories of San Diego, CA (USA) or MIDWEST MICROLAB of Indianapolis, IN (USA). Instrumentation. NMR spectra were recorded on Varian Mercury 300 (1H, 300 MHz; 13C, 75.5 MHz), Varian Mercury 400 (1H, 400 MHz; 13C, 100.7 MHz), Jeol ECA 500 (1H, 500 MHz), or Varian VX 500 (1H, 500 MHz; 13C, 125 MHz) spectrometers. 1H and 13 C{1H} NMR chemical shifts (δ) are reported in parts per million (ppm) relative to tetramethylsilane (1H and 13C, δ = 0.00 ppm), with reference to the residual proton or carbon resonance for CDCl3 (1H, δ 7.26 ppm; 13C, δ 77.16 ppm) or acetone-d6 (1H, δ = 2.05 ppm; 13C, δ = 29.84 ppm). IR spectra of isolated compounds were recorded on a Thermo-Nicolet iS10 FTIR spectrometer at room temperature. Highresolution mass spectra were recorded at the University of California, San Diego Mass Spectrometry Facility on an Agilent 6230 AccurateMass TOFMS instrument by using positive ion mode. Melting points are uncorrected and were recorded on a Stanford Research Systems EZ-Melt apparatus. (η5-C5H5)(SO2Ph)Co[κ2-OC(NMe2)CHC(SiMe3)] (8-TMS)). A toluene solution (100 mL) of 1-TMS (221 mg, 0.352 mmol) and 2-diazo-N,N-dimethylacetamide (7; 62 mg, 0.549 mmol) was heated at 70 °C for 3 h. Following chromatographic purification (silica gel, 60% acetone/hexane) and recrystallization (toluene/hexane), 8-TMS was obtained as an air-stable, dark brown, crystalline solid (56 mg, E
DOI: 10.1021/acs.organomet.8b00838 Organometallics XXXX, XXX, XXX−XXX
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Organometallics NMR Tube Reaction of 1-TMS with 2-Diazo-N,N-dimethylacetamide. An oven-dried J-Young NMR tube equipped with a Teflon needle-valve was charged with alkyne complex 1-TMS (4 mg; 0.006 mmol) and 1,3,5-tri-tert-butyl-benzene (internal standard). Dry C6D6 (0.75 mL) was distilled into the NMR tube on the Schlenk line. The sample was dissolved by shaking the tube on Vortex Mixer for 5 min and a 1H NMR spectrum was recorded. A hexane solution of 2-DiazoN,N-dimethylacetamide (7; 10%, 0.012 mmol) was added to a different oven-dried J Young NMR tube, followed by evaporation of the hexane on the Schlenk line. Dry C6D6 (0.5 mL) was then distilled into the tube and the mixture was transferred in the drybox by pipet to the NMR tube containing 1-TMS and internal standard. The reaction mixture was maintained at ambient temperature and monitored by 1H NMR spectroscopy. After 16 h, all the 1-TMS was consumed based on the disappearance of TMS resonance at δ 0.136 (s, 9H). In addition, the resonances for 8-TMS were observed at δ 0.59 (s, 9H, TMS), 2.04 (s, 3H, Me), 2.32 (s, 3H, Me), 4.85 (s, 5H, Cp), and 6.48 (s, 1H, vinyl-H). The characteristic C5H5 resonance of 12 was observed at δ 4.61 (s, 5H). The NMR yields of 8-TMS (38.5%) and 12(27.1%) were calculated by integration of the C5H5 resonances at δ 4.85 (s, 5H, 8-TMS) and 4.61 (s, 5H, 12) relative to the methyl hydrogen resonances of the internal standard at δ 1.35.
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CpCo(1,3-Diene) Complexes: An Experimental and Computational Study. Synlett 2015, 26, 2243−2246. (3) (a) O’Connor, J. M.; Chen, M.-C.; Frohn, M.; Rheingold, A. L.; Guzei, I. A. Diazoketones Undergo Reaction with a Cobalt Alkyne Complex to give Highly Functionalized Conjugated Dienes. Organometallics 1997, 16, 5589−5591. (b) O’Connor, J. M.; Chen, M.-C.; Holland, R. L.; Rheingold, A. L. Addition of Dissimilar Carbenes across an Unsymmetrically Substituted Alkyne: Regio- and Stereoselective Synthesis of Trisubstituted 1,3-Dienes. Organometallics 2011, 30, 369−371. (4) Le Paih, J.; Bray, C. V.; Derien, S.; Dixneuf, P. H. RutheniumCatalyzed Synthesis of Functional Conjugated Dienes via Addition of Two Carbene Units to Alkynes. J. Am. Chem. Soc. 2010, 132, 7391− 7397. (5) Tomioka, H.; Kondo, M.; Izawa, Y. Substituent Effects on the Product Distribution in Diazo Amide Photochemistry. Role of Ground-State Conformation Populations. J. Org. Chem. 1981, 46, 1090−1094. (6) For leading references to the metal-mediated reactions of diazoamides, see: (a) Ring, A.; Ford, A.; Maguire, A. R. Substrate and Catalyst Effects in C-H Insertion Reactions of α-Diazoacetamides. Tetrahedron Lett. 2016, 57, 5399−5406. (b) Suárez, A.; Fu, G. C. A Straightforward and Mild Synthesis of Functionalized 3-Alkynoates. Angew. Chem., Int. Ed. 2004, 43, 3580−3582. (c) Doyle, M. P.; Winchester, W. R.; Protopopova, M. N. 151. Tetrakis[(4S)-4phenyloxazolidin-2-one]dirhodium(II) and Its Catalytic Applications for Metal Carbene Transformations. Helv. Chim. Acta 1993, 76, 2227−2235. (7) For leading references to the synthesis of cobalt-diene complexes, see: (a) Aechtner, T.; Barry, D. A.; David, E.; Chellamallah, C.; Harvey, D. F.; de la Houpliere, A.; Knopp, M.; Malaska, M. J.; Pérez, D.; Schärer, K. A.; Siesel, B. A.; Vollhardt, K. P. C.; Zitterbart, R. Cobalt-Mediated [2 + 2 + 2] Cycloadditions of Alkynes to Benzo-[b]furans and Benzo[b]thiphenes: A Potential Route toward Morphanoids. Synthesis 2018, 50, 1053−1089. (b) Gandon, V.; Agenet, N.; Vollhardt, K. P. C.; Malacria, M.; Aubert, C. Cobalt-Mediated Cyclic and Linear 2:1 Cooligomerization of Alkynes with Alkenes: A DFT Study. J. Am. Chem. Soc. 2006, 128, 8509−8520. (c) Foerstner, J.; Kakoschke, A.; Stellfeldt, D.; Butenschön, H. Reactions of a Chelated Cyclopentadienylcobalt(I) Complex with 3,3-Disubstituted Cyclopropenes: Formation of Isoprene, Vinylcarbene, and 1-Phosphadiene Ligands at the Metal. Organometallics 1998, 17, 893−8966. (d) Wakatsuki, Y.; Aoki, K.; Yamazaki, H. Cobalt Metallocycles. 6. Preparation and Structure of Cobaltacyclopentene Complexes and Their Reactions with Olefins and Acetylenes. J. Am. Chem. Soc. 1979, 101, 1123−1130. (8) Dirnberger, T.; Werner, H. Hydrido(vinyl)rhodium(III)Komplexe aus [RhCl(PiPr3)2] und Olefinen. Chem. Ber. 1992, 125, 2007−2014. (9) For CpCo-sulfinato complexes, see: (a) O’Connor, J. M.; Bunker, K. D.; Rheingold, A. L.; Zakhrov, L. Sulfoxide Carbon-Sulfur Bond Activation. J. Am. Chem. Soc. 2005, 127, 4180−4181. (b) Vélez, C. L.; Markwick, P. R. L.; Holland, R. L.; DiPasquale, A. G.; Rheingold, A. L.; O’Connor, J. M. Cobalt 1,3-Diisopropyl-1Himidazol-2-ylidene Complexes: Synthesis, Solid-State Structures, and Quantum Chemistry Calculations. Organometallics 2010, 29, 6695− 6702. (10) For leading references to metal-sulfinato complexes, see: (a) Grapperhaus, C. A.; Darensbourg, M. Y. Oxygen Capture by Sulfur in Nickel Thiolates. Acc. Chem. Res. 1998, 31, 451−459. (b) Sriskandakumar, T.; Behyan, S.; Habtemariam, A.; Sadler, P. J.; Kennepohl, P. Electrophilic Activation of Oxidized sulfur Ligands and Implications for the Biological Activity of Ruthenium(II) Arene Anticancer Complexes. Inorg. Chem. 2015, 54, 11574−11580. (c) Lefort, L.; Lachicotte, R. J.; Jones, W. D. Insertion of SO2 into the Metal-Carbon Bonds of Rhodium and Iridium Compounds, and Reactivity of the SO2-Inserted Species. Organometallics 1998, 17, 1420−1425.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00838. Figures S1 and S2 (PDF) Accession Codes
CCDC 1878858−1878861 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Joseph M. O’Connor: 0000-0001-7510-3248 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We gratefully acknowledge support of the National Science Foundation (CHE-1214024 and CHE-1465079). We thank Prof. Charles Perrin for a gift of O18-enriched water.
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REFERENCES
(1) Hong, P.; Aoki, K.; Yamazaki, H. Reactions of a Diphenylacetylene-Cobalt Complex with Alkyl Diazoacetates. J. Organomet. Chem. 1978, 150, 279−293. (2) (a) O’Connor, J. M.; Ji, H.; Iranpour, M.; Rheingold, A. L. Formation of a Stable Metallacyclobutene Complex from αDiazocarbonyl and Alkyne Substrates. J. Am. Chem. Soc. 1993, 115, 1586−1588. (b) O’Connor, J. M.; Baldridge, K. K.; Vélez, C. L.; Rheingold, A. L.; Moore, C. E. Chemistry at the Alkyne−Carbene Intersection: A Metallacyclobutene−η3-Vinylcarbene Equilibration. J. Am. Chem. Soc. 2013, 135, 8826−8829. (c) Holland, R. L.; O’Connor, J. M.; Bunker, K. D.; Qin, P.; Cope, S. K.; Baldridge, K. K.; Siegel, J. S. Stereospecific Oxidative Demetallation of Highly Functionalized F
DOI: 10.1021/acs.organomet.8b00838 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics (11) (a) Niu, Q.; Zhang, S.; Li, X.; Sun, H.; Fuhr, O.; Fenske, D. Synthesis and Characterization of Diorganocobalt Chlorides by Aliphatic Vinylic C-Cl Bond Activation. Z. Anorg. Allg. Chem. 2016, 642, 866−869. (b) O’Connor, J. M.; Chen, M. C.; Holland, R. L. Protonation of Cobalt-Allene Constitutional Isomers: Highly Selective Formation of Cobalt-Allyl and Oxacobaltacyclopentadiene Complexes. Organometallics 2010, 29, 6161−6164. (c) Davies, J. E.; Mays, M. J.; Raithby, P. R.; Sarveswaran, V.; Shields, G. P. Nature of Previously Reported Thermally Unstable Products Derived from the Reaction of [Co2(CO)8] with PhSSPh, EtSSEt or PhSeSePh and of the Reactions of these Products with Alkynes or Isocyanides. J. Chem. Soc., Dalton Trans. 1998, 775−779. (d) Yamamoto, Y.; Tanase, T.; Sugano, K. Reactions of Dicobalt Octa(isocyanide) with 2Bromoacetophenone. J. Organomet. Chem. 1995, 486, 21−29. (12) King, R. B. Organometallic Chemistry of the Transition Metals. XI. Some New Cyclopentadienyl Derivatives of Cobalt and Rhodium. Inorg. Chem. 1966, 5, 82−87. (13) The crude product mixture from the reaction of 1-TMS and 7 in the presence of 18OH2-saturated C6D6 was also analyzed by ESIMS with no evidence for the formation of unlabeled 12 or isotopically enriched 12-18O. Decomposition of starting material without formation of 8-TMS and 12 was also observed in wet THF-d8 solvent. (14) (a) Cobalt complex bearing sulfoxide and sulfone substituents have been observed to undergo deoxygenation (refs 9a and 14b). (b) Holland, R. L.; O’Connor, J. M.; Rheingold, A. L. The Isolation of a Large Cyclopentadienylcobaltsulfide Cluster. The Synthesis and Crystal Structure of Octahedral closo-(η5-C5H5Co)5S. J. Cluster Sci. 2009, 20, 261−265. (15) A similar mechanism would involve initial sulfone attack on the carbene carbon of IV. (16) Minor byproducts may include cobalt-acetylides (ref 9a), dicobalt complexes (refs 1, 2b, 9a), cobalt-diene isomers (refs 2c, 15), cobaltacyclopentadienes (ref 18), and cobaltacyclobutenes (ref 2). (17) For the interconversions of diastereomeric (η5-C5H5)Co-1,3diene complexes, see: (a) Eaton, B.; King, J. A., Jr.; Vollhardt, K. P. C. First Photochemical Envelope Isomerization of a Late-TransitionMetal 1,3-Butadiene Complex: A Triple Stereochemical Labeling Experiment. J. Am. Chem. Soc. 1986, 108, 1359−1360. (b) O’Connor, J. M.; Chen, M.-C.; Rheingold, A. L. Fluoride Induced Isomerization of Cobalt Diene Complexes. Tetrahedron Lett. 1997, 30, 5241−5244. (c) Baldridge, K. K.; O’Connor, J. M.; Chen, M.-C.; Siegel, J. S. Envelope-flip Dynamics in CpCo(Diene) Complexes: An ab initio Quantum Mechanical Study. J. Phys. Chem. A 1999, 103, 10126− 10131. (18) Bunker, K. D.; Rheingold, A. L.; Moore, C. E.; Aubrey, M.; O’Connor, J. M. Synthesis of the Cobalt-alkyne Complex (η5C5H5)(PPh3)Co{η2-(Me3Si)C≡C(CO2Et)} and Structural Characterization of Trimethylsilyl Substituted Cobaltacyclopentadiene Complexes Derived Therefrom. J. Organomet. Chem. 2014, 749, 100−105.
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DOI: 10.1021/acs.organomet.8b00838 Organometallics XXXX, XXX, XXX−XXX
