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. 2019 Jul 4;9(36):21025-21030.
doi: 10.1039/c9ra03841h. eCollection 2019 Jul 1.

New molecular architectures containing low-valent cluster centres with di- and trimetalated 2-vinylpyrazine ligands: synthesis and molecular structures of Ru5(CO)15(μ5-C4H2N2CH[double bond, length as m-dash]CH)(μ-H)2 and Ru8(CO)24(μ7-C4H2N2CH[double bond, length as m-dash]C)(μ-H)3

Md Monir Hossain  1 , Nahid Akter  1 , Shishir Ghosh  1 , Vladimir N Nesterov  2 , Michael G Richmond  2 , Graeme Hogarth  3 , Shariff E Kabir  1
Affiliations

New molecular architectures containing low-valent cluster centres with di- and trimetalated 2-vinylpyrazine ligands: synthesis and molecular structures of Ru5(CO)15(μ5-C4H2N2CH[double bond, length as m-dash]CH)(μ-H)2 and Ru8(CO)24(μ7-C4H2N2CH[double bond, length as m-dash]C)(μ-H)3

Md Monir Hossain et al. RSC Adv. .

Abstract

Reaction of 2-vinylpyrazine with Ru3(CO)12 results in multiple C-H bond activations to afford penta- and octa-ruthenium clusters, Ru5(CO)15(μ5-C4H2N2CH[double bond, length as m-dash]CH)(μ-H)2 (2) and Ru8(CO)24(μ7-C4H2N2CH[double bond, length as m-dash]C)(μ-H)3 (3), in which a Ru3 sub-unit is linked to Ru2 and Ru5 centres via di- and tri-metalated 2-vinylpyrazine ligands, exhibiting novel coordination modes including the loss of ring aromaticity in 2. The bonding of 2 and the mechanism for the fluxional behaviour of the hydrides have been examined by electronic structure calculations.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Chart 1
Chart 1. Binding modes of 2-vinylpyrazine (X = N) and 2-vinylpyridine (X = CH) at polynuclear cluster centers.
Scheme 1
Scheme 1. Reaction of Ru3(CO)10(μ-dppm) with 2-vinylpyrazine.
Fig. 1
Fig. 1. Molecular structure of Ru3(CO)6(μ3-C4H3N2CHC)(μ-dppm)(μ-H)2 (1), showing 50% probability thermal ellipsoids without hydrogen atoms except the bridging hydrides (left) and the cluster core without the dppm, carbonyls and hydrogen atoms (right). Selected bond lengths (Å) and angles (°): Ru(1)–Ru(2) 2.8765(6), Ru(2)–Ru(3) 2.8264(6), Ru(1)–Ru(3) 2.7952(6), Ru(1)–P(1) 2.3273(14), Ru(3)–P(2) 2.2730(14), Ru(2)–N(1) 2.145(4), Ru(1)–C(8) 2.322(5), Ru(1)–C(7) 2.160(5), Ru(2)–C(7) 2.054(5), Ru(3)–C(7) 1.990(5), N(1)–Ru(2)–Ru(1) 83.14(11), N(1)–Ru(2)–Ru(3) 124.02(11), C(7)–Ru(1)–C(8) 36.11(19), C(7)–Ru(1)–Ru(3) 45.12(14), C(7)–Ru(3)–Ru(1) 50.28(15), Ru(1)–C(7)–Ru(3) 84.60(18).
Scheme 2
Scheme 2. Reaction of Ru3(CO)12 with 2-vinylpyrazine.
Fig. 2
Fig. 2. Molecular structure of Ru5(CO)15(μ5-C4H2N2CHCH)(μ-H)2 (2, top), showing 50% probability thermal ellipsoids without hydrogen atoms except the bridging hydrides and the cluster core without carbonyls and hydrogen atoms (bottom). Selected bond lengths (Å) and angles (°): Ru(1)–Ru(2) 2.7905(2), Ru(2)–Ru(3) 2.7742(2), Ru(1)–Ru(3) 2.9263(2), Ru(4)–Ru(5) 2.7409(2), Ru(4)–N(1) 2.1138(13), Ru(3)–N(2) 2.0850(13), Ru(1)–C(20) 2.1549(15), Ru(2)–C(20) 2.1349(15), Ru(5)–C(16) 2.2373(16), Ru(5)–C(17) 2.1858(16), Ru(5)–C(18) 2.2183(15), C(18)–N(1) 1.4425(19), C(18)–C(19) 1.448(2), C(19)–N(2) 1.284(2), C(20)–N(2) 1.4454(19), C(20)–C(21) 1.453(2), C(21)–N(1) 1.2911(19), C(16)–C(17) 1.393(2), C(17)–C(18) 1.454(2), N(2)–Ru(3)–Ru(1) 70.07(3), N(1)–Ru(4)–Ru(5) 72.10(3), Ru(1)–C(20)–Ru(2) 81.15(5).
Fig. 3
Fig. 3. Optimized structures for the isomeric hydrides based on cluster 2 (top) and potential energy profile for hydride scrambling between species A and C (bottom). Energy values (ΔG) are in kcal mol−1 with respect to A.
Fig. 4
Fig. 4. Molecular structure of Ru8(CO)24(μ7-C4H2N2CHC)(μ-H)3 (3, top), showing (a) 50% probability thermal ellipsoids without hydrogen atoms except the bridging hydrides and the cluster core without carbonyls and hydrogen atoms (bottom). Selected bond lengths (Å) and angles (°): Ru(1)–Ru(2) 2.8493(7), Ru(2)–Ru(3) 2.8585(7), Ru(1)–Ru(3) 2.8723(8), Ru(4)–Ru(5) 2.8635(7), Ru(4)–Ru(6) 2.8269(7), Ru(4)–Ru(8) 2.9769(7), Ru(5)–Ru(7) 2.8536(7), Ru(5)–Ru(8) 2.7752(7), Ru(6)–Ru(7) 2.8319(7), Ru(7)–Ru(8) 3.0470(7), Ru(2)–N(1) 2.107(4), Ru(4)–N(2) 2.102(4), Ru(3)–C(28) 2.097(5), Ru(4)–C(25) 2.114(5), Ru(5)–C(25) 2.109(5), Ru(6)–C(25) 2.107(5), Ru(7)–C(25) 2.148(5), Ru(6)–C(26) 2.201(5), C(28)–N(1) 1.336(7), C(28)–C(27) 1.429(7), C(27)–N(2) 1.351(7), C(29)–N(2) 1.349(7), C(29)–C(30) 1.368(8), C(30)–N(1) 1.340(7), C(25)–C(26) 1.447(7), C(26)–C(27) 1.450(8), Ru(5)–Ru(4)–Ru(6) 92.857(19), Ru(6)–Ru(4)–Ru(8) 91.39(2), Ru(4)–Ru(5)–Ru(7) 81.786(18), Ru(4)–Ru(6)–Ru(7) 82.815(18), Ru(5)–Ru(7)–Ru(6) 92.961(19), Ru(6)–Ru(7)–Ru(8) 89.86(2), Ru(4)–Ru(8)–Ru(7) 76.815(18).
Scheme 3
Scheme 3. Hydride scrambling between species A and C through intermediate B.
Scheme 4
Scheme 4. Proposed scheme for the formation of 1–3.
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