Modular Synthesis of Fischer Biscarbene Complexes of Chromium

Article pubs.acs.org/Organometallics

Modular Synthesis of Fischer Biscarbene Complexes of Chromium Hana Váňová,† Tomás ̌ Tobrman,† Irena Hoskovcová,‡ and Dalimil Dvořaḱ *,† †

Department of Organic Chemistry and ‡Department of Inorganic Chemistry, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic S Supporting Information *

ABSTRACT: Aromatic and (hetero)aromatic chromium aminocarbenes were lithiated on the (hetero)aromatic ring and transmetalated with ZnBr2. The subsequent Pd(PPh3)4- or PdCl2(XantPhos)-catalyzed Negishi reaction with dibromoarenes or chromium alkoxy-/aminocarbenes bearing bromine atoms yielded bisaminocarbene or mixed bisalkoxyaminocarbene complexes of chromium. This methodology allows easy access to the biscarbene complexes containing poly(hetero)aromatic bridges, such as biphenylene, bithienylene, tetrathienylene, 1,1′-ferrocenylene, and others. In total, 18 new biscarbene complexes, including two containing both chromium and tungsten, were synthesized in this fashion. The electrochemical behavior of the biscarbenes obtained exhibits electronic communication between the metals.

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INTRODUCTION Since their discovery by Fischer and Maasböl,1 Fischer monocarbene complexes (especially those of Cr, Mo, and W) have found numerous applications in the synthesis of complicated organic molecules.2 In addition to the organic synthesis, Fischer carbene complexes have recently attracted the attention of material chemists as electron acceptors in the construction of molecules with nonlinear optical properties,3 bioconjugates,4 and organometallic gelators.5 In addition, the electrochemical behavior of Fischer carbene complexes has attracted considerable attention.6 On the other hand, the chemistry of Fischer-type biscarbene complexes is much less developed. There are several examples of their synthetic exploration,7 and a number of biscarbenes with carbene moieties connected with a conjugated bridge7h,8 and polymetallic carbene complexes9 were synthesized and studied for their potential use in materials chemistry. However, the potential of these compounds still remains largely unexplored. The reason the chemistry of bis- and oligocarbene complexes remains underdeveloped in comparison to that of their monocarbene counterparts might be their limited accessibility.2e These complexes have been mostly prepared in the classical way, by the introduction of a carbene moiety to the preformed skeleton.1,10 Recently we have shown that aminocarbene complexes containing aromatic or heteroaromatic groups can be lithiated. The subsequent reaction with electrophiles11 allows the preparation of functionalized carbene complexes and, after transmetalation to zinc, Negishi crosscoupling reactions.12 Herein we report that the cross-coupling methodology can be also used for the synthesis of different types of biscarbene complexes, including those containing both alkoxy- and aminocarbene moieties, in which two carbene groups are connected with a (hetero)aromatic bridge. This approach thus allows the modular synthesis of biscarbene © 2016 American Chemical Society

complexes from preformed parts already containing carbene groups.

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RESULTS AND DISCUSSION Due to the tendency of alkoxycarbene complexes to add organolithiums,13 only aminocarbene complexes can be successfully metalated.11 Thus, chromium aminocarbene complexes 1a−d were lithiated with BuLi and, after transmetalation with ZnBr2, subjected to Pd(PPh3)4-catalyzed coupling with a thiophene-derived bromoethoxycarbene complex of chromium 2a (Scheme 1). The yields of the obtained mixed alkoxy-amino biscarbene complexes 3a−d were high, with the exception of the furyl derivative 3b, which was obtained in 47% yield (Table 1, entry 2). All of the obtained mixed carbene complexes were smoothly converted to the bisaminocarbenes 4a−d by reaction with dimethylamine in THF in medium isolated yields (Scheme 1 and Table 1). Next we turned our attention to the coupling of metalated 1a with (hetero)aromatic dihalides. Depending on the ratio of reagents, it should be possible, in principle, to prepare symmetric biscarbenes or halogenated monocarbenes with the possibility of further derivatization. Thus, the reaction of metalated 1a with 1,4-diiodobenzene in a 0.9:1 ratio under Pd(PPh3)4 catalysis gave mixture of the monocarbene 5a-I (50%) and biscarbene 6a (30%), (Scheme 2). The same reaction furnished the biscarbene 6a in 60% yield when 2 equiv of 1a were used. The attempts to couple an excess (2.4 equiv) of the zincated 1a with easily accessible dibromo derivatives such as 1,4dibromobenzene, 1,3-dibromobenzene, 4,4′-dibromo-1,1′-biphenyl, 2,5-dibromothiophene, 3,4-dibromothiophene, and 1,1′-dibromoferrocene in cross-coupling reactions have failed Received: June 29, 2016 Published: August 23, 2016 2999

DOI: 10.1021/acs.organomet.6b00527 Organometallics 2016, 35, 2999−3006

Article

Organometallics Scheme 1. Cross-Coupling of Metalated Aminocarbene Complexes 1 with Bromoethoxycarbene 2a

Scheme 3. Cross-Coupling of Aminocarbene 1a with (Hetero)aromatic Dibromides

Table 2. Cross-Coupling Reaction of an Excess (2.4 equiv) of Metalated 1a with (Hetero)aromatic Dibromides (Scheme 3) Table 1. Cross-Coupling Reactions of Zincated Heterocyclic Aminocarbenes 1 with Bromoethoxycarbene 2a (Scheme 1)

a

entry

X

Y

3, yield (%)a

4, yield (%)a

1 2 3 4

S O NMe CHCH

H H Br Br

3a, 90 3b, 47 3c, 76 3d, 70

4a, 71 4b, 60 4c, 65 4d, 62

Isolated yield.

Scheme 2. Cross-Coupling Reaction of Zincated Aminocarbene 1a with 1,4-Diiodobenzene

a

Isolated yield. bAn inseparable mixture of starting 1a and monocoupled product was obtained. cAn inseparable mixture of the products of homocoupling, 4a and 6a, was obtained. dAn inseparable mixture of products was formed; only starting 1a was isolated (17% yield). eStarting dibromide was completely recovered together with the starting 1a (57%) and the product of homocoupling, 4a (16%).

of mono- and bis-coupled products in low yield, while 1,1′dibromoferrocene and 3,4-dibromothiophene failed to give any biscarbene under these conditions. While the metalation of alkoxycarbene complexes was not possible, the opposite approach, coupling of (4-bromophenyl)zinc(II) bromide or 5-bromothiophen-2-yl)zinc(II) bromide with the alkoxybromocarbene 2a, has been successful, giving the corresponding bromoalkoxycarbenes 7a-Br and 7d-Br, respectively, in high yields. The reaction with dimethylamine then yielded high levels of the corresponding dimethylaminocarbene complexes 5a-Br and 5d-Br (Scheme 4). The reactions using (3-bromophenyl)zinc(II) bromide or (4′-bromo-[1,1′biphenyl]-4-yl)zinc(II) bromide under the above conditions have not been successful. The obtained iodocarbene complex 5a-I and bromocarbene complexes 5a-Br and 5d-Br were metalated and again subjected to coupling with bromoalkoxycarbene 2a, yielding mixed

to provide any carbene product under the above conditions. However, Pd(Xantphos)Cl2, which proved to be effective also in previous cross-couplings of carbene complexes,12 gave better results. Thus, 1,3-dibromobenzene, 4,4′-dibromo-1,1′-biphenyl, and 2,5-dibromothiophene afforded the desired biscarbenes 6 in low to medium yields (Scheme 3 and Table 2, entries 2−4) accompanied by variable amounts of the corresponding products of monocoupling (5-Br) and homocoupling (4a) together with starting 1a (see the Experimental Section). In contrast, 1,4-dibromobenzene afforded an inseparable mixture 3000


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Organometallics

5a-I in comparison with that of the bromo derivative 5a-Br (Scheme 5). In the case of the coupling of metalated bromothiophene carbene 5d-Br with 2a, in addition to the expected mixed carbene 8d, also a substantial amount of the product of homocoupling of 5d-Br, the tetrathienylene bisaminocarbene complex 9, was obtained. The direct coupling of 5d-Br with metalated 5d-Br under Pd(Xantphos)Cl2 catalysis resulted in an 81% isolated yield of 9 (Scheme 6). In addition, monometalated 1,1′-dibromoferrocene was successfully coupled with 2a. Under Pd(PPh3)4 catalysis formation of the monocarbene 7f-Br together with a small amount (9%) of the bisalkoxycarbene 10 was observed using a slight excess (1.1 equiv) of 2a. The obtained alkoxycarbene complex 7f was then smoothly converted to the corresponding dimethylaminocarbene complex 5f-Br. Using Pd(PPh3)4 the metalated bromocarbene 5f-Br was successfully coupled with another 2a, furnishing mixed carbene 8f in 58% yield. Subsequent reaction of 8f with dimethylamine afforded the corresponding bisaminocarbene complex 11 in low yield (Scheme 7).

Scheme 4. Cross-Coupling of Monozincated (Hetero)aryl Dibromides with Bromoethoxycarbene 2a

aminoalkoxycarbene complexes 8a,d containing 1,4-phenylene bridges (Scheme 5) and 2,5-thienylene bridges (Scheme 6), Scheme 5. Cross-Coupling of Metalated Halocarbene Complexes 5a-I and 5-Br with Bromoethoxycarbene 2a

Scheme 7. Synthesis of Ferrocene-Derived Mono- and Biscarbenes

Scheme 6. Cross-Coupling of Metalated Complex 5d-Br with Bromoethoxycarbene 2a and Homocoupling of 5d-Br

Unfortunately, attempts to extend the above cross-coupling procedure to the preparation of biscarbene complexes of other group 6 elements have met with only very limited success. Thus, the zincated molybdenum and tungsten analogues of 1a coupled with 2a afforded less than 10% of the desired products. The opposite approach, the coupling of metalated 1a with the tungsten derived bromocarbene 2b, has been more fruitful, giving the expected biscarbene complex 12 in 55% yield (Scheme 8). This result is consistent with our previous findings that the coupling of 2b with organozinc reagents proceeded

respectively. The 1,4-phenylene-bridged complex 8a was obtained in somewhat higher yield from the iododerivative 3001


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Organometallics

complicated nature. In comparison with that of the monocarbene 1a, the reduction of all studied biscarbenes was easier, as it takes part at less negative potentials. The difference went up to 430 mV for molecules with two dimethylamino groups and even to 730 mV for aminoethoxycarbene 3a (Table 3). The reduction of 3a was easier due to the presence of an ethoxy group.15 While the first reduction step of 3a was chemically reversible,16 the compounds 4a, 6d, and 9 were reduced irreversibly.

Scheme 8. Formation of Mixed Chromium−Tungsten Biscarbene Complexes 12 and 13

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CONCLUSION The Negishi reaction is the method of choice for the preparation of bisamino and bis(alkoxyamino) complexes of chromium containing an aromatic or heteroaromatic bridge. In the case of chromium, the coupling of metalated aminocarbenes both with bromoaminocarbenes and with bromoethoxycarbenes is possible. In addition, coupling of the metalated thiophene-derived chromium aminocarbene complex 1a with the bromoethoxycarbene group of tungsten 2b was successful. In contrast, the reaction of zincated aminocarbene complexes of molybdenum and tungsten with the bromoethoxycarbene group of chromium has failed. Our electrochemical study revealed that the oxidation of the biscarbenes proceeds exclusively on the electronically communicating metal centers. In comparison to the monocarbene 1a, the reduction of the oligothienyl bis-carbenes 3a, 4a, 6d, and 9 proceeds much more easily, showing the significant participation of the bridge. Detailed electrochemical studies, as well as studies of the reactivity of the obtained complexes, are currently under way in our laboratories.

easily.12 Subsequent conversion of 12 to the bisaminocarbene 13 was also smooth. Electrochemistry. A previous electrochemical study on chromium, tungsten, and iron monocarbene complexes showed that these molecules contain two rather independent electrochemically active centers. The reduction center is situated on the carbene carbon, and its reduction potential Ered depends on the carbene carbon substitution. On the other hand, the oxidation occurs on the metal atom and its oxidation potential Eox reflects electron density on it.6h This picture is in agreement with their HOMO and LUMO composition. Biscarbenes contain two oxidation centers which could communicate electronically via the bridge. That kind of communication can be identified by the occurrence of two subsequent oxidation signals, whereas in the absence of electronic communication both metals are oxidized at the same potential.14 The reduction process of biscarbenes is influenced by the reducibility of the bridge itself and by its participation in the LUMO. A previous comparison of Ered values of 4a and its monocarbene analogue 1a showed that the reduction of the biscarbene becomes easier by 430 mV.17 Representative examples of the complexes prepared above, the biscarbenes 3a, 4a, 6d, and 9, were subjected to a preliminary electrochemical study. The oxidation proceeded in two steps in all cases. This shows successive oxidation of two metal centers communicating electronically via a conjugated bridge. The first step was found to be chemically reversible for 9; in all other cases an irreversible process took place. The oxidation potentials of the first step were slightly lower than that of the monocarbene 1a, but the difference in oxidation potentials within the series did not exceed 40 mV (Table 3). The reduction, which was studied by polarography, proceeds in several (at least three) subsequent steps of somewhat

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Table 3. Reduction and Oxidation Potentials of Biscarbene Complexes 3a, 4a, 6d, and 9 and the Monocarbene 1a oxidation, Epa (V)a

a

carbene

reduction, E1/2 (V)

3a 4a 6d 9 1a

−1.00 −1.30 −1.34, −1.42 −1.40, −1.47 −1.73

a

+0.81 +0.82 +0.79 +0.78 +0.83

EXPERIMENTAL SECTION

General Information. All reactions were performed under an argon atmosphere. The solvents were dried and degassed by standard procedures; silica gel (Merck, Geduran Si 60, 63−200 μm) was used for column chromatography. Pentacarbonyl[(N,N-dimethylamino)(2thienyl)carbene]chromium(0) (1a), 17 pentacarbonyl[(N,Ndimethylamino)(2-furyl)carbene]chromium(0) (1b),17 pentacarbonyl[(N,N-dimethylamino)(5-bromo-1-methyl-2-pyrrolyl)carbene]chromium(0) (1c), 11 pentacarbonyl[(N,N-dimethylamino)(4bromophenyl)carbene]chromium(0) (1d),7f pentacarbonyl[ethoxy(5bromo-2-thienyl)methylene]chromium(0) (2a),12 and pentacarbonyl[ethoxy(5-bromo-2-thienyl)methylene]tungsten(0) (2b)12 were prepared by the reported procedures; other compounds were purchased. Electrochemical measurements were carried out in a 10 mL cell of Metrohm type, in extra dry acetonitrile (99.9%, water 108 °C dec. 1H NMR (CDCl3): δ 1.70 (t, J = 6.9 Hz, 3H, CH3), 3.31 (s, 3H, CH3), 4.01 (s, 3H, CH3), 5.16 (q, J = 6.9 Hz, 2H, CH2), 6.50 (d, J = 3.9 Hz, 1H, CH), 7.28 (d, J = 3.9 Hz, 1H, CH), 7.30 (d, J = 3.9 Hz, 1H, CH), 8.18 (d, J = 4.2 Hz, 1H, CH). 13C{1H} NMR (acetone-d6): δ 15.4 (CH3-Et), 47.7 (NCH3), 52.2 (NCH3), 77.4 (OCH2), 120.9, 126.5, 128.1, 135.1, 144.4, 147.5, 152.8, 155.4, 217.6 (CO), 218.0 (CO), 224.5 (CO), 224.6 (CO), 262.3 (C), 311.6 (C). IR (ATR): ν 2050 (s), 1981 (w), 1900 (s), 1536 (w), 1420 (m), 1353 (w), 1291 (w), 1209 (m), 1187 (w), 1059 (w), 1011 (w) cm −1 . Anal. Calcd for C24H15CrNO11S2: C, 43.58; H, 2.29; N, 2.12; S, 9.69. Found: C, 43.82; H, 2.11; N, 2.08; S, 9.72. Amino-Ethoxy Biscarbene 3b. The general procedure A starting from 1b (0.158 g, 0.50 mmol), and ethoxycarbene complex 2a (0.247 g, 0.60 mmol) followed by column chromatography (silica gel, hexane) afforded 0.150 g of the title compound (47%) as a dark red foam. 1H NMR (CDCl3): δ 1.71 (t, J = 6.9 Hz, 3H, CH3), 3.46 (s, 3H, CH3), 4.01 (s, 3H, CH3), 5.18 (q, J = 7.2 Hz, 2H, CH2), 6.35 (d, J = 3.6 Hz, 2H, CH), 6.86 (d, J = 3.6 Hz, 1H, CH), 7.47 (d, J = 4.2 Hz, 2H, CH), 8.22 (d, J = 4.2 Hz, 1H, CH). 13C{1H} NMR (CDCl3): δ 15.6 (CH3Et), 48.8 (NCH3), 52.1 (NCH3), 76.2 (OCH2), 109.8, 111.1, 125.3, 141.2, 142.8, 149.2, 153.4, 159.3, 217.2 (CO), 217.5 (CO), 223.8 (CO), 224.0 (CO), 259.5 (C), 312.9 (C). IR (ATR): ν 2051 (m), 1872 (s), 1706 (m), 1521 (w), 1419 (m), 1175 (m), 1068 (w), 1010 (w) cm−1. Anal. Calcd for C24H15CrNO12S: C, 44.66; H, 2.34; N, 2.17; S, 4.97. Found: C, 44.92; H, 2.39; N, 2.11; S, 4.94. Amino-Ethoxy Biscarbene 3c. The general procedure A starting from 1c (0.122 g, 0.30 mmol) and ethoxycarbene complex 2a (0.148 g, 0.36 mmol) followed by column chromatography (silica gel, hexane) afforded 0.150 g of the title compound (76%) as a dark violet foam. 1H NMR (CDCl3): δ 1.67 (t, J = 7.2 Hz, 3H, CH3), 3.16 (s, 3H, CH3), 3.52 (s, 3H, CH3), 4.04 (s, 3H, CH3), 5.14 (q, J = 7.2 Hz, 2H, CH2), 5.92 (d, J = 3.9 Hz, 2H, CH), 6.68 (d, J = 3.9 Hz, 1H, CH), 7.21 (d, J = 4.5 Hz, 2H, CH), 8.22 (d, J = 4.2 Hz, 1H, CH). 13C{1H} NMR (CDCl3): δ 15.5 (CH3-Et), 33.3 (NCH3-Pyr), 46.9 (NCH3), 50.9 (OCH2), 75.7 (NCH3), 103.6, 113.8, 125.4, 143.1, 145.0, 146.9, 151.5, 153.5, 216.8 (CO), 217.6 (CO), 223.6 (CO), 272.7 (C), 330.9 ( C). IR (ATR): ν 2051 (s), 1980 (w), 1899 (s), 1701 (w), 1597 (w), 1524 (w), 1421 (m), 1391 (m), 1293 (w), 1067 (w) cm−1. Anal. Calcd for C25H18Cr2N2O11S: C, 45.60; H, 2.76; N, 4.25; S, 4.87. Found: C, 45.36; H, 3.11; N, 4.65; S, 4.41. Amino-Ethoxy Biscarbene 3d. The general procedure A starting from 1d (0.121 g, 0.30 mmol) and ethoxycarbene complex 2a (0.148 g, 0.36 mmol) followed by column chromatography (silica gel, hexane) afforded 0.130 g of the title compound (70%) as a dark red foam. 1H NMR (CDCl3): δ 1.71 (t, J = 7.2 Hz, 3H, CH3), 3.12 (s, 3H, CH3), 4.02 (s, 3H, CH3), 5.19 (q, J = 7.2 Hz, 2H, CH2), 6.79 (d, J = 8.7 Hz, 2H, CH), 7.47 (d, J = 4.2 Hz, 1H, CH), 7.75 (d, J = 9 Hz, 2H, CH), 8.24 (d, J = 4.5 Hz, 1H, CH). 13C{1H} NMR (CDCl3): δ 15.1 (CH3Et), 46.1 (NCH3), 51.2 (NCH3), 75.8 (OCH2), 119.8, 124.9, 126.7, 130.4, 142.5, 153.0, 153.06, 153.13, 216.9 (CO), 217.1 (CO), 223.4 (CO), 223.6 (CO), 273.7 (C), 312.7 (C). IR (ATR): ν 2052 (s), 1882 (s), 1536 (w), 1427 (m), 1253 (w), 1177 (m), 1065 (w), 1010 (w) cm−1. Anal. Calcd for C26H17CrNO11S: C, 47.64; H, 2.61; N, 2.14; S, 4.89. Found: C, 47.91; H, 2.59; N, 1.96; S, 4.82.

Amino-Ethoxy Biscarbene 8a. The general procedure A starting from 5a-Br (0.200 g, 0.4 mmol), and ethoxycarbene complex 2a (0.180 g, 0.44 mmol) followed by column chromatography (silica gel, hexane) afforded 0.100 g of the title compound (34%) as a dark red foam. Alternatively, the title compound was prepared via the general procedure A starting from 5a-I (0.200 g, 0.37 mmol) and ethoxycarbene complex 2a (0.168 g, 0.41 mmol) followed by column chromatography (silica gel, hexane), affording 0.113 g (41%) of the title compound. 1H NMR (CDCl3): δ 1.72 (t, J = 7.2 Hz, 3H, CH3), 3.32 (s, 3H, CH3), 4.02 (s, 3H, CH3), 5.19 (q, J = 7.2 Hz, 2H, CH2), 6.53 (d, J = 3.6 Hz, 1H, CH), 7.28 (d, J = 3.6 Hz, 1H, CH), 7.49 (d, J = 4.5 Hz, 1H, CH), 7.63 (d, J = 9 Hz, 2H, CH), 7.72 (d, J = 8.7 Hz, 2H, CH), 8.26 (d, J = 4.2 Hz, 1H, CH). 13C{1H} NMR (acetone-d6): δ 14.5 (CH3-Et), 46.5 (NCH3), 51.3 (NCH3), 76.5 (OCH2), 119.7, 124.1, 125.2, 125.6, 125.8, 126.9, 129.0, 131.7, 135.1, 141.6, 143.3, 152.9, 153.0, 153.4, 216.9 (CO), 217.1 (CO), 223.7 (CO), 262.5 ( C), 311.9 (C). IR (ATR): ν 2053 (s), 1899 (s), 1703 (w), 1596 (w), 1427 (m), 1255 (w), 1177 (m), 1066 (w), 1010 (w) cm−1. Anal. Calcd for C30H19CrNO11S2: C, 48.85; H, 2.60; N, 1.90; S, 8.69. Found: C, 48.33; H, 3.03; N, 1.83; S, 8.69. Amino-Ethoxy Biscarbene 8d. The general procedure A starting from 5d-Br (0.240 g, 0.48 mmol) and ethoxycarbene complex 2a (0.218 g, 0.53 mmol) followed by column chromatography (silica gel, hexane/DCM 4/1) afforded 0.203 g of the title compound (57%) as a dark violet foam. 1H NMR (CDCl3): δ 1.68 (t, J = 6.8 Hz, 3H, CH3), 3.32 (s, 3H, CH3), 4.01 (s, 3H, CH3), 5.17 (q, J = 6.8 Hz, 2H, CH2), 6.47 (d, J = 3.6 Hz, 1H, CH), 7.11 (m, 2H, CH), 7.29 (d, J = 4.8 Hz, 1H, CH), 7.32 (d, J = 3.6, 1H, CH), 8.20 (d, J = 4.4 Hz, 1H, CH). 13 C{1H} NMR (CDCl3): δ 15.2 (CH3-Et), 46.9 (NCH3), 51.4 (NCH3), 75.7 (OCH2), 119.2, 124.4, 124.9, 125.1, 127.2, 135.0, 135.4, 138.4, 142.8, 146.3, 152.0, 152.1, 216.6 (CO), 217.1 (CO), 223.3 (CO), 223.4 (CO), 268.9 (C), 311.3 (C). IR (ATR): ν 2051 (s), 1980 (w), 1890 (s), 1527 (w), 1420 (m), 1175 (w), 1099 (w), 1052 (w) cm−1. Anal. Calcd for C28H17Cr2NO11S3: C, 45.23; H, 2.30; N, 1.88; S, 12.93. Found: C, 45.29; H, 2.41; N, 1.75; S, 13.04. Amino-Ethoxy Biscarbene 8f. The general procedure A starting from 5f-Br (0.110 g, 0.16 mmol) and ethoxycarbene complex 2a (0.074 g, 0.18 mmol) followed by column chromatography (silica gel, hexane/DCM 1/1) afforded 0.079 g of the title compound (58%) as a violet amorphous solid. 1H NMR (CDCl3): δ 1.70 (t, J = 6.8 Hz, 3H, CH3), 3.28 (s, 3H, CH3), 3.99 (s, 3H, CH3), 4.28 (t, J = 2 Hz, 2H, CH), 4.41 (quint, J = 2 Hz, 4H, CH), 4.56 (t, J = 2 Hz, 2H, CH), 5.14 (q, J = 6.8 Hz, 2H, CH2), 6.36 (d, J = 3.6 Hz, 1H, CH), 6.72 (d, J = 3.6 Hz, 1H, CH), 7.03 (d, J = 4.4 Hz, 1H, CH), 8.12 (d, J = 4.4 Hz, 1H, CH). 13C{1H} NMR (CDCl3): δ 15.3 (CH3-Et), 46.8 (NCH3), 51.4 (NCH3), 69.1, 69.8, 71.3, 72.7, 75.4, 78.4, 80.8, 119.1, 122.4, 124.9, 140.7, 143.1, 150.5, 151.3, 155.5, 216.9 (CO), 217.3 (CO), 223.3 (CO), 223.4 (CO), 269.4 (C), 308.6 (C). IR (ATR): ν 2922 (w), 2052 (s), 1965 (m), 1890 (s), 1612 (w) 1522 (w), 1462 (m), 1419 (m), 1318 (w), 1263 (w), 1241 (w), 1148 (m), 1078 (w), 1058 (w) cm−1. Anal. Calcd for C34H23Cr2FeNO11S2: C, 48.30; H, 2.74; N, 1.66; S, 7.58. Found: C, 48.36; H, 3.49; N, 1.51; S, 7.12. General Procedure B: Conversion of the Ethoxycarbene Complexes to the Aminocarbenes. A solution of dimethylamine (2 equiv, 2 M in ether) was added to a solution of 3a−d, 5a-Br, 5d-Br, 6d, 5f-Br, or 8f in THF (10 mL/mmol). The mixture was stirred for 1 h at room temperature, alumina (3 g/mmol) was added, the solvents were evaporated in vacuo, and the product was isolated by column chromatography on silica gel. Bisaminocarbene Complex 4a. The general procedure B starting from 3a (0.180 g, 0.27 mmol) and a solution of dimethylamine (0.27 mL) followed by column chromatography (silica gel, hexane/DCM 1/ 1) afforded 0.127 g of the title compound (71%) as a yellow crystalline solid. Mp: >115 °C dec. 1H NMR (CDCl3): δ 3.32 (s, 6H, CH3), 4.00 (s, 6H, CH3), 6.44 (d, J = 3.6 Hz, 2H, CH), 7.03 (d, J = 3.6 Hz, 1H, CH). 13C{1H} NMR (acetone-d6): δ 46.7 (NCH3), 51.4 (NCH3), 119.4, 123.6, 135.3, 151.9, 217.0 (CO), 223.7 (CO), 262.1 (C). Anal. Calcd for C24H16CrN2O10S2: C, 43.64; H, 2.44; N, 4.24; S, 9.71. Found: C, 43.59; H, 2.58; N, 4.09; S, 9.49. 3003


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Organometallics Bisaminocarbene Complex 4b. The general procedure B starting from 3b (0.100 g, 0.16 mmol) and a solution of dimethylamine (0.16 mL) followed by column chromatography (silica gel, hexane/DCM 1/ 1) afforded 0.060 g of the title compound (60%) as a yellow foam. 1H NMR (CDCl3): δ 3.31 (s, 3H, CH3), 3.49 (s, 3H, CH3), 3.98 (s, 6H, CH3), 6.34 (d, J = 3.6 Hz, 1H, CH), 6.48 (d, J = 3.9 Hz, 1H, CH), 6.57 (d, J = 3.9 Hz, 1H, CH), 7.27 (d, J = 3.6 Hz, 1H, CH). 13C{1H} NMR (CDCl3): δ 47.4 (NCH3), 48.8 (NCH3), 51.9 (NCH3), 52.3 (NCH3), 107.4, 110.9, 119.7, 124.4, 131.7, 150.2, 152.5, 157.9, 217.0 (CO), 217.6 (CO), 223.9 (CO), 224.3 (CO), 257.3 (C), 269.2 ( C). Anal. Calcd for C24H16CrN2O11S: C, 44.73; H, 2.50; N, 4.35; S, 4.98. Found: C, 44.30; H, 2.87; N, 4.01; S, 5.36. Bisaminocarbene Complex 4c. The general procedure B starting from 3c (0.150 g, 0.22 mmol) and a solution of dimethylamine (0.22 mL) followed by column chromatography (silica gel, hexane/DCM 1/ 1) afforded 0.090 g of the title compound (65%) as a yellow foam. 1H NMR (CDCl3): δ 3.16 (s, 3H, CH3), 3.33 (s, 3H, CH3), 3.37 (s, 3H, CH3), 3.99 (s, 3H, CH3), 4.02 (s, 3H, CH3), 5.86 (d, J = 3.9 Hz, 1H, CH), 6.35 (d, J = 3.9 Hz, 1H, CH), 6.49 (d, J = 3.6 Hz, 1H, CH), 6.86 (d, J = 3.6 Hz, 1H, CH). 13C{1H} NMR (acetone-d6): δ 31.9 (NCH3Pyr), 46.2 (NCH3), 46.5 (NCH3), 50.5 (NCH3), 51.3 (NCH3), 101.8, 110.3, 118.8, 124.7, 125.8, 133.6, 145.1, 152.3, 216.9 (CO), 217.0 (CO), 223.8 (CO), 223.9 (CO), 262.3 (C), 265.6 (C). Anal. Calcd for C25H19CrN3O10S: C, 45.67; H, 2.91; N, 6.39; S, 4.88. Found: C, 45.97; H, 3.21; N, 6.43; S, 4.94. Bisaminocarbene Complex 4d. The general procedure B starting from 3d (0.130 g, 0.21 mmol) and a solution of dimethylamine (0.21 mL) followed by column chromatography (silica gel, hexane/DCM 1/ 1) afforded 0.080 g of the title compound (62%) as a yellow crystalline solid. Mp: >93 °C dec. 1H NMR (CDCl3): δ 3.10 (s, 3H, CH3), 3.31 (s, 3H, CH3), 4.01 (s, 6H, CH3), 6.51 (d, J = 3.6 Hz, 2H, CH), 6.74 (d, J = 8.1 Hz, 2H, CH), 7.22 (d, J = 3.3 Hz, 1H, CH), 7.61 (d, J = 8.4 Hz, 2H, CH). 13C{1H} NMR (CDCl3): δ 46.1 (NCH3), 46.8 (NCH3), 51.3 (NCH3), 51.4 (NCH3), 119.3, 119.7, 122.9, 125.7, 131.1, 142.4, 151.7, 216.8 (CO), 217.1 (CO), 223.5 (CO), 223.6 (CO), 269.3 ( C), 274.7 (C). Anal. Calcd for C26H18CrN2O10S: C, 47.71; H, 2.77; N, 4.28; S, 4.90. Found: C, 47.85; H, 2.88; N, 4.16; S, 4.72. Bromoaminocarbene Complex 5a-Br. The general procedure B starting from 7a-Br (0.400 g, 0.82 mmol) and a solution of dimethylamine (0.82 mL) followed by column chromatography (silica gel, hexane/DCM 2/1) afforded 0.386 g of the title compound (96%) as a yellow crystalline solid. Mp: >95 °C dec. 1H NMR (CDCl3): δ 3.31 (s, 3H, CH3), 4.00 (s, 3H, CH3), 6.49 (d, J = 3.9 Hz, 1H, CH), 7.18 (d, J = 3.6 Hz, 1H, CH), 7.43 (d, J = 8.4 Hz, 2H, CH), 7.51 (d, J = 9 Hz, 2H, CH). 13C{1H} NMR (acetone-d6): δ 46.5 (NCH3), 51.3 (NCH3), 119.5, 120.8, 123.7, 127.0, 132.0, 132.8, 141.3, 152.7, 216.9 (CO), 223.7 (CO), 262.5 (C). Anal. Calcd for C18H12BrCrNO5S: C, 44.46; H, 2.49; N, 2.88; S, 6.59. Found: C, 44.37; H, 2.39; N, 2.82; S, 6.74. Bromoaminocarbene Complex 5d-Br. The general procedure B starting from 7d-Br (0.130 g, 0.26 mmol) and a solution of dimethylamine (0.13 mL) followed by column chromatography (silica gel, hexane/DCM 2/1) afforded 0.092 g of the title compound (71%) as a yellow crystalline solid. Mp: >127 °C dec. 1H NMR (CDCl3): δ 3.30 (s, 3H, CH3), 4.00 (s, 3H, CH3), 6.42 (d, J = 3.9 Hz, 1H, CH), 6.90 (d, J = 3.6 Hz, 1H, CH), 6.98 (t, J = 3.6 Hz, 2H, CH). 13C{1H} NMR (CDCl3): δ 46.5 (NCH3), 51.1 (NCH3), 111.0, 118.7, 123.4, 123.7, 130.4, 135.0, 137.4, 151.1, 216.3 (CO), 223.1 (CO), 268.9 ( C). Anal. Calcd for C16H10BrCrNO5S2: C, 39.04; H, 2.05; N, 2.85; S, 13.03. Found: C, 39.03; H, 2.08; N, 2.86; S, 13.60. Bromoaminocarbene Complex 5f-Br. The general procedure B starting from 7f-Br (0.190 g, 0.32 mmol) and a solution of dimethylamine (0.32 mL) followed by column chromatography (silica gel, hexane/DCM 1/1) afforded 0.120 g of the title compound (63%) as an orange crystalline solid. Mp: >123 °C dec. 1H NMR (CDCl3): δ 3.31 (s, 3H, CH3), 3.99 (s, 3H, CH3), 4.04 (t, J = 1.8 Hz, 2H, CH), 4.27 (t, J = 1.8 Hz, 2H, CH), 4.36 (t, J = 1.5 Hz, 2H, CH), 4.56 (t, J = 1.8 Hz, 2H, CH), 6.38 (d, J = 3.9 Hz, 1H, CH), 6.93 (d, J = 3.6 Hz, 1H, CH). 13C{1H} NMR (CDCl3, 75): δ 46.7 (NCH3), 51.3 (NCH3), 66.3, 66.7, 69.0, 69.3, 71.4, 72.1, 78.4, 80.8, 118.9, 122.5, 141.1, 150.5,

216.9 (CO), 223.6 (CO), 269.3 (C). Anal. Calcd for C22H16BrCrFeNO5S: C, 44.47; H, 2.71; N, 2.36; S, 5.40. Found: C, 44.56; H, 2.86; N, 2.38; S, 5.61. Ferrocene-Derived Bisaminocarbene Complex 11. The general procedure B starting from 8f (0.170 g, 0.2 mmol) and a solution of dimethylamine (0.2 mL) followed by column chromatography (silica gel, hexane/DCM 1/1) afforded 0.040 g of the title compound (24%) as a yellow amorphous solid. 1H NMR (CDCl3): δ 3.29 (s, 6H, CH3), 3.98 (s, 6H, CH3), 4.26 (t, J = 2.4 Hz, 4H, CH), 4.36 (t, J = 2.4 Hz, 4H, CH), 6.37 (d, J = 3.6 Hz, 2H, CH), 6.82 (d, J = 3.6 Hz, 2H, CH). 13 C NMR (CDCl3): δ 46.8, 51.4, 69.0, 70.8, 80.2, 119.1, 122.3, 141.9, 150.3, 217.0, 223.6, 269.4. Anal. Calcd for C34H24Cr2FeN2O10S2: C, 48.36; H, 2.86; N, 3.32; S, 7.59. Found: C, 48.54; H, 2.95; N, 3.13; S, 7.72. Mixed Chromium−Tungsten Diaminocarbene Complex 13. The general procedure B starting from 12 (0.04 g, 0.05 mmol) and a solution of dimethylamine (0.1 mL) followed by column chromatography (silica gel, hexane/DCM 2/1) afforded 0.017 g of the title compound (43%) as a yellow crystalline solid. Mp: >125 °C dec. 1H NMR (CDCl3): δ 3.31 (s, 3H, CH3), 3.32 (s, 3H, CH3), 3.93 (s, 3H, CH3), 4.00 (s, 3H, CH3), 6.44 (d, J = 3 Hz, 1H, CH), 6.50 (d, J = 2.7 Hz, 1H, CH), 7.05 (m, 2H, CH). 13C{1H} NMR (CDCl3): δ 45.4 (NCH3), 46.9 (NCH3), 51.4 (NCH3), 53.9 (NCH3), 119.1, 120.0, 123.5, 123.8, 135.3, 135.7, 151.4, 152.6, 198.1 (J183W−13C = 128 Hz) (CO), 203.6 (CO), 216.7 (CO), 223.4 (CO), 249.3 (C), 269.3 ( C). IR (ATR): ν 2921 (w), 2851 (w), 2059 (m), 2050 (m), 2879 (s), 1662 (w), 1599 (m), 1536 (w), 1489 (w), 1444 (w), 1398 (w), 1201 (w), 1157 (w) cm−1. Anal. Calcd for C24H16CrN2O10S2W: C, 36.38; H, 2.04; N, 3.54; S, 8.09. Found: C, 36.59; H, 2.56; N, 3.29; S, 8.21. General procedure C: Preparation of Bromoalkoxycarbene Complexes 7a-Br, 7d-Br, and 7f-Br. Butyllithium (1.1 equiv, 2.5 M in hexanes) was added to a solution of dihalogenated compound (1.0 equiv) in dry THF (10 mL/mmol) cooled to −78 °C. The resultant mixture was stirred for 30 min at −78 °C followed by addition of a solution of ZnBr2 (1.0 equiv) in dry THF (6 mL/mmol). After 30 min at −78 °C, a solution of 2a (1.1 equiv) and Pd(PPh3)4 (5 mol %) in dry THF (6 mL/mmol) was added. The resultant mixture was warmed to ambient temperature and stirred for 2 h with exclusion of light. The mixture was then quenched with water, the organic layer was separated, and the water layer was extracted with ether. The combined organic layers were dried (MgSO4), alumina (3 g/1 mmol) was added, and the solvents were evaporated in vacuo. The crude product was subjected to column chromatography. Bromoalkoxycarbene 7a-Br. The general procedure C starting from 1,4-dibromobenzene (0.236 g, 1 mmol) and ethoxycarbene complex 2a (0.452 g, 1.1 mmol) followed by column chromatography (silica gel, hexane) afforded 0.440 g of the title compound (90%) as a dark red crystalline solid. Mp: >136 °C dec. 1H NMR (CDCl3): δ 1.69 (t, J = 6.9 Hz, 3H, CH3), 5.19 (q, J = 7.2 Hz, 2H, CH2), 7.44 (d, J = 4.2 Hz, 1H, CH), 7.55 (s, 4H, CH), 8.23 (d, J = 4.2 Hz, 1H, CH). 13 C{1H} NMR (CDCl3): δ 15.2 (CH3-Et), 75.8 (OCH2), 123.8, 125.2, 126.4, 127.7, 129.1, 131.9, 132.3, 142.5, 152.1, 153.5, 217.1 (CO), 223.3 (CO), 313.7 (C). Anal. Calcd for C18H11BrCrO6S: C, 44.37; H, 2.28; S, 6.58. Found: C, 44.18; H, 1.95; S, 6.38. Bromoalkoxycarbene 7d-Br. The general procedure C starting from 2,5-dibromothiophene (0.24 mL, 2 mmol) and ethoxycarbene complex 2a (0.904 g, 2.2 mmol) followed by column chromatography (silica gel, hexane) afforded 0.810 g of the title compound (82%) as a dark red crystalline solid. Mp: >149 °C dec. 1H NMR (CDCl3): δ 1.70 (t, J = 6.9 Hz, 3H, CH3), 5.17 (q, J = 6.9 Hz, 2H, CH2), 7.05 (d, J = 3.9 Hz, 1H, CH), 7.16 (d, J = 4.2 Hz, 1H, CH), 7.24 (d, J = 4.2 Hz, 1H, CH), 8.17 (d, J = 4.5 Hz, 1H, CH). 13C{1H} NMR (CDCl3): 15.2 (CH3-Et), 75.8 (OCH2), 114.5, 125.2, 126.3, 131.3, 137.6, 142.5, 145.4, 152.4, 217.1 (CO), 223.3 (CO), 312.7 (C). Anal. Calcd for C16H9BrCrO6S2: C, 38.96; H, 1.84; S, 13.00. Found: C, 39.15; H, 1.75; S, 13.55. Bromoalkoxycarbene 7f-Br and Bisethoxycarbene Complex 10. The general procedure C starting from 1,1′-dibromoferrocene (0.344 g, 1 mmol) and ethoxycarbene complex 2a (0.452 g, 1.1 mmol) followed by column chromatography (silica gel, hexane) afforded 3004


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Organometallics 0.520 g of the 7f-Br (87%) as a dark red crystalline solid followed by 10 (hexane/DCM 4/1), 0.050 g (10%) which was obtained as a dark violet crystalline solid. Data for 7f-Br are as follows. Mp: 104 °C. 1H NMR (CDCl3): δ 1.71 (t, J = 6.9 Hz, 3H, CH3), 4.07 (t, J = 2.1 Hz, 2H, CH), 4.33 (t, J = 2.1 Hz, 2H, CH), 4.52 (t, J = 2.1 Hz, 2H, CH), 4.71 (t, J = 2.1 Hz, 2H, CH), 5.14 (q, J = 7.2 Hz, 2H, CH2), 7.19 (d, J = 4.2 Hz, 1H, CH), 8.15 (d, J = 4.5 Hz, 1H, CH). 13C{1H} NMR (CDCl3): δ 15.4 (CH3-Et), 68.0, 69.8, 70.1, 70.8, 72.6, 73.2, 75.7, 78.9, 79.2, 125.3, 128.6, 128.9, 133.8, 134.0, 143.1, 151.8, 154.9, 217.5 (CO), 223.5 (CO), 309.6 (C). Anal. Calcd for C22H15BrCrFeO6S: C, 44.90; H, 2.54; S, 5.39. Found: C, 45.15; H, 2.48; S, 5.68. Data for 10 are as follows. Mp: 141 °C dec. 1H NMR (CDCl3): δ 1.70 (t, J = 6.8 Hz, 6H, CH3), 4.43 (t, J = 2 Hz, 4H, CH), 4.60 (t, J = 2 Hz, 4H, CH), 5.14 (q, J = 7.2 Hz, 4H, CH2), 6.89 (d, J = 4.8 Hz, 2H, CH), 8.06 (d, J = 4.4 Hz, 2H, CH). 13C{1H} NMR (CDCl3): δ 15.3 (CH3Et), 69.9, 72.8, 75.5, 79.0, 124.9, 142.5, 151.8, 154.0, 217.3 (CO), 223.2 (CO), 309.8 (C). Anal. Calcd for C34H22Cr2FeO12S2: C, 48.34; H, 2.62; S, 7.57. Found: C, 48.88; H, 2.75; S, 7.26. General Procedure D: Cross-Coupling of 1a with (Hetero)aromatic Dihalo Derivatives. Butyllithium (1.1 equiv, 2.5 M in hexanes) was added to a solution of aminocarbene complex 1a (1.0 equiv) in dry THF (10 mL/mmol) cooled to −78 °C. The resultant mixture was stirred for 30 min at −78 °C followed by addition of a solution of ZnBr2 (1.0 equiv) in dry THF (6 mL/mmol). After 30 min at −78 °C, a solution of dihalogenated compound (0.4 equiv) and Pd(XanthPhos)Cl2 (5 mol %) in dry THF (6 mL/mmol) was added. The resultant mixture was warmed to ambient temperature and stirred for 2 h with exclusion of light. The mixture was then quenched with water, the organic layer was separated, and the water layer was extracted with ether. The combined organic layers were dried (MgSO4), alumina (3 g/1 mmol) was added, and the solvents were evaporated in vacuo. The crude product was subjected to column chromatography. Bisaminocarbene Complex 6c. The general procedure D starting from 1a (0.159 g, 0.48 mmol) and 4,4′-dibromobiphenyl (0.063 g, 0.2 mmol) followed by column chromatography (silica gel, hexane/DCM 1/1) afforded 0.055 g of the title compound (34%) as an orange crystalline solid. Mp: >127 °C dec. 1H NMR (CDCl3): δ 3.33 (s, 6H, CH3), 4.02 (s, 6H, CH3), 6.53 (d, J = 3.3 Hz, 2H, CH), 7.26 (d, J = 4.2 Hz, 2H, CH), 7.64 (s, 8H, CH). 13C{1H} NMR (CDCl3): δ 46.8 (NCH3), 51.4 (NCH3), 119.4, 123.0, 126.0, 127.3, 132.7, 139.6, 142.8, 151.9, 216.8 (CO), 223.5 (CO), 269.7 (C). IR (ATR): ν 2051 (m), 1965 (w), 1881 (s), 1602 (m), 1534 (m), 1488 (w), 1448 (w), 1395 (m), 1255 (w), 1204 (w) cm−1. Anal. Calcd for C36H24Cr2N2O10S2: C, 53.20; H, 2.98; N, 3.45; S, 7.89. Found: C, 53.51; H, 3.23; N, 3.44; S, 8.17. Bisaminocarbene Complex 6d. The general procedure D starting from 1a (0.159 g, 0.48 mmol) and 2,5-dibromothiophene (0.024 mL, 0.2 mmol) followed by column chromatography (silica gel, hexane/ DCM 2/1) afforded 0.080 g of the title compound (54%) as an orange foam. 1H NMR (CDCl3): δ 3.31 (s, 6H, CH3), 4.00 (s, 6H, CH3), 6.45 (d, J = 3.6 Hz, 2H, CH), 7.05 (s, 4H, CH). 13C{1H} NMR (CDCl3): δ 47.1 (NCH3), 51.7 (NCH3), 119.5, 123.8, 124.8, 135.7, 136.2, 151.6, 217.0 (CO), 223.8 (CO), 269.2 (C). Anal. Calcd for C28H18Cr2N2O10S3: C, 45.29; H, 2.44; N, 3.77; S, 12.95. Found: C, 45.49; H, 2.89; N, 3.79; S, 12.44. Bisaminocarbene Complex 6f. The general procedure D starting from 1a (159 g, 0.48 mmol) and 1,3-dibromobenzene (0.024 mL, 0.2 mmol) followed by column chromatography (silica gel, hexane/DCM 2/1) afforded 0.080 g of the title compound (54%) as an orange foam. 1 H NMR (CDCl3): δ 3.32 (s, 6H, CH3), 4.01 (s, 6H, CH3), 6.53 (d, J = 2.4 Hz, 2H, CH), 7.26 (d, J = 3 Hz, 2H, CH), 7.47 (m, 3H, CH), 7.72 (s, 1H, CH). 13C{1H} NMR (CDCl3): δ 46.8 (NCH3), 51.4 (NCH3), 119.3, 122.7, 123.4, 125.0, 129.6, 134.3, 142.5, 152.1, 216.8 (CO), 223.6 (CO), 269.4 (C). Anal. Calcd for C30H20Cr2N2O10S2: C, 48.92; H, 2.74; N, 3.80; S, 8.70. Found: C, 48.72; H, 3.31; N, 3.90; S, 9.23. Iodoaminocarbene Complex 5a-I and Bisaminocarbene Complex 6a. The general procedure D starting from butyllithium (1.2 mmol, 0.54 mL, 2.24 M in hexanes), carbene complex 1a (0.331 g, 1

mmol), ZnBr2 (0.250 g, 1 mmol), 1,4-diiodobenzene (0.363 g, 1.1 mmol), Pd(PPh3)4 (0.060 g, 0.05 mmol), and dry THF (22 mL) followed by column chromatography (silica gel, hexane/DCM 2/1) afforded 0.250 g (50%) of the iodocarbene 5a-I (first fraction) and 0.110 g (30%) of the biscarbene 6a (second fraction). Data for 5a-I are as follows. Yellow crystalline solid. Mp: >75 °C dec. 1H NMR (CDCl3): δ 3.30 (s, 3H, CH3), 4.00 (s, 3H, CH3), 6.49 (d, J = 3.9 Hz, 1H, CH), 7.19 (d, J = 3.6 Hz, 1H, CH), 7.31 (d, J = 8.4 Hz, 2H, CH), 7.71 (d, J = 8.4 Hz, 2H, CH). 13C{1H} NMR (acetone-d6): δ 46.5 (NCH3), 51.3 (NCH3), 119.5, 123.7, 127.0, 133.2, 138.1, 139.5, 141.4, 152.7, 216.9 (CO), 223.7 (CO), 262.5 (C). Anal. Calcd for C18H12CrINO5S: C, 40.54; H, 2.27; N, 2.63; S, 6.01. Found: C, 40.22; H, 2.12; N, 2.49; S, 5.76. Data for 6a are as follows. Yellow crystalline solid. Mp: >90 °C dec. 1H NMR (CDCl3): δ 3.32 (s, 6H, CH3), 4.01 (s, 6H, CH3), 6.52 (d, J = 3.6 Hz, 2H, CH), 7.23 (d, J = 3.6 Hz, 2H, CH), 7.56 (s, 4H, CH). 13C{1H} NMR (acetone-d6): δ 46.5 (NCH3), 51.3 (NCH3), 119.6, 123.3, 125.8, 132.9, 142.2, 152.4, 216.9 (CO), 223.7 (CO), 262.5 (C). Anal. Calcd for C30H20CrN2O10S2: C, 48.92; H, 2.74; N, 3.80; S, 8.71. Found: C, 48.65; H, 2.63; N, 3.75; S, 8.91. Bromoaminocarbene Complex 5c. The general procedure D starting from butyllithium (0.22 mL, 0.55 mmol, 2.5 M in hexanes), aminocarbene complex 1a (0.165 g, 0.5 mmol), ZnBr2 (0.125 g), Pd(XanthPhos)Cl2 (0.020 g, 0.025 mmol), 4,4′-dibromobiphenyl (0.187 g, 0.6 mmol), and dry THF (11 mL) cooled to −78 °C followed by column chromatography (silica gel, hexane/DCM 2/1) afforded 0.118 g of the title compound (42%) as a yellow crystalline solid. Mp: >153 °C dec. 1H NMR (CDCl3): δ 3.33 (s, 3H, CH3), 4.02 (s, 3H, CH3), 6.52 (d, J = 3.6 Hz, 1H, CH), 7.25 (d, J = 3.9 Hz, 1H, CH), 7.65 (m, 8H, CH). 13C{1H} NMR (CDCl3): δ 46.8 (NCH3), 51.4 (NCH3), 119.4, 121.8, 123.1, 126.0, 127.4, 128.5, 132.0, 132.9, 139.3, 142.6, 152.0, 216.8 (CO), 223.5 (CO), 269.8 (C). Anal. Calcd for C24H16BrCrNO5S: C, 51.26; H, 2.87; N, 2.49; S, 5.70. Found: C, 51.20; H, 2.79; N, 2.44; S, 5.69. Bisaminocarbene Complex 9. The general procedure D starting from butyllithium (1 mmol, 0.4 mL, 2.5 M in hexanes), aminocarbene complex 5d-Br (0.443 g, 0.9 mmol), ZnBr2 (0.228 g, 0.9 mmol), aminocarbene complex 5d-Br (0.492 g, 1 mmol), Pd(XanthPhos)Cl2 (0.036 g, 0.045 mmol) and dry THF (22 mL) followed by column chromatography (silica gel, hexane/DCM 1/2) afforded 0.600 g of the title compound (81%) as an orange crystalline solid. Mp: >113 °C dec. 1 H NMR (CDCl3): δ 3.32 (s, 6H, CH3), 4.00 (s, 6H, CH3), 6.45 (d, J = 3.6 Hz, 2H, CH), 7.08 (m, 6H, CH). 13C{1H} NMR (CDCl3): δ 46.6 (NCH3), 51.1 (NCH3), 118.9, 123.2, 124.1, 124.3, 135.0, 135.7, 150.9, 216.4 (CO), 223.1 (CO), 269.0 (C). IR (ATR): ν 3067 (w), 2950 (w), 2052 (m), 1943 (m), 1877 (s), 1531 (m), 1498 (w), 1398 (w), 1155 (w), 1099 (w), 1023 (w) cm−1. Anal. Calcd for C32H20Cr2N2O10S4: C, 46.60; H, 2.44; N, 3.40; S, 15.05. Found: C, 46.40; H, 2.32; N, 3.06; S, 14.88. Mixed Chromium−Tungsten Alkoxy-Aminocarbene Complex 12. The general procedure A starting from butyllithium (0.22 mL, 0.55 mmol, 2.5 M in hexanes), 1a (0.165 g, 0.5 mmol), ZnBr2 (0.125 g), carbene complex 2b (0.300 g, 0.55 mmol), Pd(PPh3)4 (0.030 g, 0.025 mmol) in dry THF (5 mL), and dry THF (11 mL) followed by column chromatography (silica gel, hexane/DCM 4/1) afforded 0.220 g of the title compound (55%) as a red crystalline solid. Mp: >147 °C dec. 1H NMR (CDCl3): δ 1.68 (t, J = 7.2 Hz, 3H, CH3), 3.31 (s, 3H, CH3), 4.02 (s, 3H, CH3), 4.98 (q, J = 6.9 Hz, 2H, CH2), 6.50 (d, J = 3.9 Hz, 1H, CH), 7.27 (d, J = 4.5 Hz, 1H, CH), 7.33 (d, J = 3.9 Hz, 1H, CH), 8.10 (d, J = 4.2 Hz, 1H, CH). 13C{1H} NMR (CDCl3): δ 15.1 (CH3-Et), 46.8 (NCH3), 51.5 (NCH3), 78.1 (OCH2), 119.4, 125.0, 126.4, 135.0, 143.4, 146.7, 153.4, 155.4, 197.4 (J183W−13C = 127 Hz) (CO), 202.3 (CO), 216.7 (CO), 223.1 (CO), 269.0 (C), 286.3 (C). IR (ATR): ν 2061 (m), 2052 (m), 1883 (s), 1521 (w), 1421 (m), 1356 (w), 1291 (w), 1242 (w), 1211 (w), 1166 (w), 1068 (w), 1011 (w) cm−1. Anal. Calcd for C24H15CrNO11S2W: C, 36.34; H, 1.91; N, 1.77; S, 8.08. Found: C, 36.47; H, 1.85; N, 1.73; S, 8.29. 3005


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Organometallics

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00527. Polarograms of the carbene complexes 1a, 3a, 4a, 6d, and 9 (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail for D.D.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Ministry of Education, Youth and Sports of the Czech Republic (Specific university research No 20/2015 and No 20/2016) for financial support.

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REFERENCES

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Modular Synthesis of Fischer Biscarbene Complexes of Chromium

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