Methimazolyl based diptych bicyclo-[3.3.0]-ruthenaboratranes

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Methimazolyl based diptych bicyclo-[3.3.0]-

ruthenaboratranes†

Cite this: DOI: 10.1039/c8dt04813d

Chenxi Ma and Anthony F. Hill

*

The reactions of [RuCl(R)(CO)(PPh₃)₂] (R = CHvCHPh, Ph) with Na[H₂B(mt)₂] (mt = N-methyl-2-mercap-

toimidazolyl) transiently provide [Ru(R)(CO)(PPh₃){κ³-H,S,S’-H₂B(mt)₂}] which each evolve to the ruthena-

boratrane [Ru(CO)(PPh₃)₂{κ³-B,S,S’-BH(mt)₂}](Ru→B)⁸. The phosphine ligands may be selectively replaced

to provide the complexes [Ru(CO)(L)(PPh₃){κ³-B,S,S’-BH(mt)₂}] (L = CO, PMe₂Ph) and [Ru(CO)L₂{κ³-B,S,S’-

BH(mt)₂}] (L = PMe₂Ph, P(OMe)₃, L₂= Z-Ph₂PCHvCHPPh₂) with, in each case, retention of the ruthenium–

boron dative bond.

Received 6th December 2018,

Accepted 4th January 2019

DOI: 10.1039/c8dt04813d

rsc.li/dalton

(Chart 1), however these remain comparatively rare, based

Introduction

either on N-heterocyclic buttresses¹¹or Bourissou’s 2-phosphi-

The term ‘metallaboratrane’ has been coined to draw analogy noaryl system.^7,12To these may be added a small number of

between the first such compound [Ru(CO)(PPh₃){κ⁴-B,S,S′,S″-B potentially triptych systems in which one buttress, however,

(mt)₃}] (mt = N-methylmercaptoimidazolyl),^1,2and Brown’s remains pendant, at least in the solid state.^11a,13The majority

boratrane B(OCH₂CH₂)₃N,³given that both tricyclo-[3.3.3.0] of these involve the heavier (4d or 5d) group 9 and 10 metals.

cage structures include

a

trans-annular dative (polar A recurrent feature of the Ar–B(C₆H₄PR₂)₂(R = ⁱPr, Ph; Ar = Ph,

C₆H₂Me₃) system, in particular for 3d metals Fe, Co and Ni, is

covalent,^4,5M → B cf. N → B) bond (Chart 1).

A large number of tricyclo-[3.3.3.0] metallaboratranes are the η²-B,C(ipso) or ‘η³-B,C,C′-bora-allyl’ type coordination^12a–c,e

now known based on cages in which the buttresses are var- of the B-aryl group. This is reminiscent of η³-benzyl ligands,

iants on the original N-heterocycle (mt)⁶or alternatively, and provides a means by which coordinative unsaturation at

2-phosphinoaryl bridges as pioneered by Bourissou.⁷It might the metal may be alleviated. Diptych bicyclo-[3.3.0] metallabor-

be argued that the presence of the trans-annular M → B inter- atranes are of interest in that the metal–boron interaction is

action is in part a simple corollary of the geometric constraints not constrained within the more restrictive tricyclo-[3.3.3.0]

imposed by the cage. Indeed, a recent attempt to assay the triptych geometry, allowing more confidence in interrogating

strength of this interaction through correlation of structural the nature of the M → B bond. Furthermore, the more exposed

and spectroscopic data for an extensive series of the tri-but- M → B bond has been found to play a non-innocent role in the

tressed (‘triptych’) ruthenaboratranes [Ru(CO)L{κ⁴-B,S,S′,S″-B

(mt)₃}] (L = PPh₃, CO, CN^tBu, CNC₆H₂Me₃, PMe₃, PMe₂Ph,

P(OMe)₃, P(OPh)₃, PCy₃) was generally unsuccessful,⁸conclud-

ing that subtleties in the Ru → B bonding might be out-

weighed by inter- and intramolecular non-bonding inter-

actions and cage strain.

Dibutressed (‘diptych’) boratranes are not only well-known⁹

but also enjoy practical application in organic synthesis, most

notably the B(O₂CCH₂)₂NMe group found in BMIDA borates.¹⁰

Within the field of metallaboratrane chemistry, a number of

dibuttressed ‘diptych’ metallaboratranes have been isolated

Research School of Chemistry, Australian National University, Acton, Canberra,

A.C.T., Australia. E-mail: a.hill@anu.edu.au

†Electronic supplementary information (ESI) available: Selected characterisa-

tional spectra; crystallographic information files. CCDC 1881115–1881118,

1881121–1881125, 1881156. For ESI and crystallographic data in CIF or other

electronic format see DOI: 10.1039/c8dt04813d

Chart 1 (a) Triptych and (b) diptych boratranes and metallaboratranes.

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activation of diatomic ligands such as CS,¹⁴H₂,^12a,cCO^12aand

N₂.^12e

Given that the majority of diptych metallaboratranes have

emerged within groups 9 and 10, with the only group 8

examples being those based on Peters’ [Fe(CO)_n{BPh

(C₆H₄PⁱPr₂-2)₂}]^x−(n = 2, 3; x = 0, 1, 2) ferraboratranes,^12a–fwe

have now revisited the archetypal zerovalent⁵ruthenium

system to establish whether methimazolyl diptych ruthenabor-

atranes might also be viable.

Results and discussion

Synthesis and reactivity

The triptych ruthenaboratrane [Ru(CO)(PPh₃){κ⁴-B,S,S′,S″-B

(mt)₃}] (1a) arose from the reactions of [RuCl(R)(CO)(PPh₃)₂] (R

= Ph,¹⁵CHvCHPh¹⁶) with Na[HB(mt)₃],^1awhich were pre-

sumed to proceed via the complexes [Ru(R)(CO)(PPh₃){HB

(mt)₃}] (R = Ph 2a, CHvCHPh 2b) although these could not be

isolated. In contrast the reactions of [RuHCl(CO)(PPh₃)₃] with

either Na[HB(mt)₃] or Na[H₂B(mt)₂]¹⁷aﬀorded the stable

hydrido complexes [RuH(CO)(PPh₃){κ³-H,S,S′-HBR(mt)₂}] (R =

H 2c, mt 3).^1b,18The κ³-H,S,S′ coordination mode has in the

interim been found to be favourable for a wide range of tran-

sition metals and is especially prevalent within the chemistry

of ruthenium.^18,19In extending studies on this mode of coordi-

nation, we recently described the series of complexes [RuR(CO)

(PPh₃){κ³-H,S,S′-H₂B(mt)₂}] (R = H 2c, Cl 4a, SeH 4b, SePh 4c,

SiCl₃4d, SiMe₃4e, BO₂C₆H₄4f),¹⁸none of which underwent

the B–H activation step required for the installation of the

metallaboratrane cage. In contrast, whilst the σ-organyl deriva-

Fig. 1 Molecular structure of 5 in a crystal of 5·Et₂O (hydrogen atoms

and Et₂O solvent omitted, phenyl groups simpliﬁed, 50% displacement

ellipsoids). Data collected using both Mo-Kα and Cu-Kα radiation

selected bond lengths (Å) and angles (°) derived from Cu-Kα data: B1–

Ru1 2.2463(16), B1–H1 1.17(2), Ru1–P1 2.4766(4), Ru1–P2 2.3045(4),

Ru1–C1 1.8336(16), H1–B1–Ru1 123.3(13), N2–B1–H1 104.7(12), N3–B1–

H1 106.1(12), B1–Ru1–P1 166.36(4), B1–Ru1–P2 84.13(4), P1–Ru1–P2

108.061(13). Inset = space ﬁlling representations showing PPh₃ligands

in lilac and green.

The initial synthesis of 5 involved employing the phenyl

precursor [RuCl(Ph)(CO)(PPh₃)₂] which also resulted in the for-

mation of a side product [Ru(Ph)(CO)(κ²-N,S-mt)(PPh₃)₂] (6)

and its removal by extensive washing with diethyl ether some-

what compromised the isolated yield of 5 (34%). The complex

6 has been described previously by Wilton-Ely including a crys-

tallographic study of a dichloromethane solvate.²¹The deter-

mination of the crystal structure of unsolvated 6 is presented

in the Experimental section but calls for no further comment.

Given that the synthesis of [RuCl(Ph)(CO)(PPh₃)₂] requires the

undesirable use of diphenyl mercury, an alternative more con-

venient and higher yielding synthesis of 5 was developed

directly from mer-[RuHCl(CO)(PPh₃)₃] (7). The reaction of 7

with ethynylbenzene to aﬀord the trans-β-styryl complex [RuCl

(CHvCHPh)(CO)(PPh₃)₂] is rapid and essentially quantitat-

ive,¹⁶such that successive treatment of 7 with HCuCPh and

Na[H₂B(mt)₂] returned 5 in 61% yield (3 g scale, ‘one pot’).

The low symmetry of complex 5 (C₁) follows from the

tives [RuR(CO)(PPh₃){κ³-H,S,S′-H₂B(mt)₂}] (R

=

Ph 4g,

CHvCHPh 4h) could be spectroscopically observed (see

Experimental), they eluded isolation due to their spontaneous

evolution into what we now identify as the diptych

ruthenaboratrane [Ru(CO)(PPh₃)₂{κ³-B,S,S′-BH(mt)₂}](Ru→B)⁸(5)

(Scheme 1, Fig. 1).²⁰

1

appearance of two distinct methyl resonances in the H NMR

spectrum (δ_H= 3.07, 3.33), as well as four imidazolyl peaks (δ_H

3

= 6.04, 6.15, 6.50, 6.58 d × 4, J_HH= 1.8 Hz) indicating the

chemical inequivalence of the two methimazolyl arms, which

was also evident from ¹³C{¹H} NMR data. Despite the broaden-

ing of the borohydride resonance by the quadrupolar boron

nuclei (¹⁰B and ¹¹B), the BH resonance was identified at δ_H

=

4.07 (h.h.w. = 209 Hz). A single boron resonance (¹¹B{¹H}: δ_B=

4.12) was observed in a region consistent with four-coordinate

metal-bound boron.^1,2The two phosphine environments were

manifest as resonances at δ_P= 19.3 and 52.7, where the broad-

ness of the latter resonance was indicative of coordination

trans to the boron. The composition of complex 5 was further

Scheme 1 Synthesis of a diptych ruthenaboratrane.

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supported in the HR-ESI(+ve ion, MOH matrix) mass spectrum

with a peak corresponding to a [M − CO + OMe]⁺adduct (m/z

= 895.1592).

The formulation of 5 was confirmed by an X-ray crystallo-

graphic study, the results of which are summarised in Fig. 1.

This reveals a distorted octahedral coordination at ruthenium

and distorted tetrahedral geometry about boron with angles in

the range of 104.7(12)–123.2(13)°. The Ru1–B1 bond length of

2.2463(16) Å is somewhat longer than found in the corres-

ponding triptych analogue 1a (2.161(5) Å; Δ = 17 e.s.d.), falling

outside the range previously observed for Ru → B bonds (2.157

(6)–2.184(6) Å).^1,8

Notably, the two Ru–P bonds are very significantly diﬀerent

in length (430 e.s.d.), where the phosphine trans to boron exhi-

bits a far longer bond than that trans to sulfur. The compara-

tively pronounced trans influence of M → B bonds has been

noted previously for the complexes [Rh(PMe₃)₂{B(mt)₃}]⁺,

[PtI₂{B(mt)₃}] and [Fe(CO)₂{B(mt^tBu)₃}] wherein the boron and

one thione donor are trans to identical σ-donor (PMe₃),²²(σ +

π) donor (iodide)²³or π-acceptor (CO)²⁴ligands.

Scheme 2 Mechanism conjecture to account for the formation of a

borato alkynyl complex 8.

The formation of a minor side product (8, ca. 1%) was

observed to accompany the isolation of 5 when the ‘one-pot’ observed cleavage of ruthenium alkenyls by terminal alkynes

procedure was used and whilst this was only isolated in to provide σ-alkynyl derivatives, a process that underpins

suﬃcient quantity for crystallographic characterisation, details the catalytic dimerization of terminal alkynes to provide

are included here as they provide two relevant points of inter- butenynes.²⁵The first possibility is that a small amount of

est. The product was identified as the alkynyl complex [Ru unreacted [RuHCl(CO)(PPh₃)₃] remained at the time Na[H₂B

(CuCPh)(CO)(PPh₃){κ³-H,S,S′-H₂B(mt)₂}] (8, Fig. 2) which is (mt)₂] was added (the alkyne hydroruthenation is also a revers-

akin to the complexes 2c and 4a–f but distinct from 4g and 4h ible process), being converted to 2c followed by alkyne hydro-

in being a thermally stable σ-organyl derivative that does not metallation to generate 4h which then undergoes (net) σ-meta-

evolve to 5.

thesis with ethynylbenzene to generate the alkynyl complex 8.

Notably, treating 5 with an excess of ethynylbenzene does This may be excluded because it could be shown in separate

not lead to formation of 8 under the conditions in which it experiments that pre-isolated 2c is unreactive towards

was first isolated (Scheme 2). This leaves two possible mechan- HCuCPh under these conditions. Under more forcing con-

istic routes to 8, both of which involve the occasionally ditions, with an excess of HCuCPh, the hydride precursor

[RuHCl(CO)(PPh₃)₃] aﬀords [RuCl{C(CuCPh)vCHPh}(CO)-

(PPh₃)₂],²⁶which is an eﬀective alkyne dimerization catalyst.²⁷

The yet to be isolated species ‘RuCl(CuCPh)(CO)(PPh₃)_n’

(n = 2, 3) being plausible resting states that might react with

Na[H₂B(mt)₂] to aﬀord 8. The mild conditions under which 8

forms would seem to argue against this. The final mechanism,

which we consider the most plausible, involves a reaction of

4h with HCuCPh to provide 8 and styrene, in a process that

operates to a very modest extent in competition with the metal-

laboratrane formation.

The structural features of 8 (Fig. 2) correlate well with those

reported for the analogous complexes 2c and 4a–4f and call for

little comment other than to note that the Ru⋯B separation of

2.740(2) Å falls within the range previously observed (cf.

2.651–2.897 Å), as does the less precisely determined B–H–Ru

angle of 134(3)° (cf. 128–138°).¹⁸The Ru–C and C–C bonds are

Fig. 2 Molecular structure of 8 in a crystal of 8·CHCl₃(hydrocarbon also well within the ranges observed for the copious structural

hydrogen atoms and CHCl₃solvent omitted, phenyl groups simpliﬁed,

50% displacement ellipsoids). Selected bond lengths (Å) and angles (°):

B1⋯Ru1 2.740(2), B1–H1 1.24(4), B1–H2 1.19(4), Ru1–H1 1.74(4), Ru1–P1

2.3228(6), Ru1–C1 1.864(2), Ru1–C2 2.028(3), C2–C3 1.200(4), C3–C4

1.448(3), B1–H1–Ru1 134(3), H1–Ru1–C2 173.3(14), S2–Ru1–P1 176.25

(2), S1–Ru1–P1 87.20(2), S1–Ru1–S2 89.82(2).

data available for octahedral ruthenium(^II) alkynyls.

The potential of the M → B association to engage directly in

reactions has been long of interest. In particular, the question

of interconversion between coordination modes κ³-B,S,S′ and

κ³-H,S,S′ via hydride migration from the metal centre was first

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demonstrated when the platinaboratrane [PtH{P(C₆H₄Me-4)₃}

{B(mt)₃}]Cl was shown to undergo phosphine substitution by

PMe₃or PEt₃accompanied by reconstitution of the κ³-H,S,S′-

HB(mt)₃coordination.²⁵In the interim, further examples of

hydrogenation of M → B bonds have emerged,^{11h,i,12d,f,i,13b}

some of which involve heterolytic cleavage of dihydrogen itself

to generate metal hydride (M − H^δ+) and boron-hydride (M −

H

^δ−) units. Taken together, the complexes [Co(H₂){κ⁴-B,P,P′,P″-

B(C₆H₄PⁱPr₂-2)₃}]^12eand [MH(CO)_x{κ³-H,P,P′-HB(C₆H₂Me₃)

(C₆H₄PⁱPr₂)₂}] [M = Ni, x = 0;^12cM = Fe x = 2^12a] provide an

elegant indication of the subtleties at play along the dihydro-

gen cleavage trajectory.

As noted above, 5 fails to react with ethynylbenzene to

aﬀord 8 and in a similar manner, no reaction is observed

between 5 and HBO₂C₆H₄(HBCat), dihydrogen, or penta-

methylcyclopentadiene even though plausible products of

such reactions [RuH(CO)(PPh₃){H₂B(mt)₂}] (2c), [Ru(BCat)(CO)

(PPh₃){H₂B(mt)₂}] (4f)¹⁸and [Ru{H₂B(mt)₂}(η-C₅Me₅)] are all

known and stable.^19hIn contrast, treating 5 with one equi-

valent of hydrogen chloride results in extensive decomposition

and degradation of the cage such that a mixture of products

was obtained within one hour (distribution invariant over

24 hours) with complete consumption of 5. Numerous reso-

nances were observed in the ³¹P{¹H} NMR spectrum (δ_P= 19.1,

28.1, 35.7, 45.2, 50.0 and 55.2) none of which predominated or

corresponded to the anticipated chloro complex [RuCl(CO)

(PPh₃){H₂B(mt)₂}] (4a: δ_P= 36.3; δ_H= −18.11; δ_B= −7.36).¹⁸

Attempts to identify the products formed through crystallisa-

tion of the crude mixture from chloroform/n-pentane aﬀorded

complexes 9 and 10 as a mixture, which could be further puri-

fied to exclusively isolate 10 (Scheme 3).

Fig. 3 Molecular structure of 9 in a crystal of 9·CHCl₃(CHCl₃solvent

omitted, phenyl groups simpliﬁed, 50% displacement ellipsoids).

Selected bond lengths (Å) and angles (°): Ru1–Cl1 2.4351(6), Ru1–Cl2

2.4841(6), Ru1–S1 2.3845(6), Ru1–P1 2.3982(6), Ru1–P2 2.4239(6), Ru1–

C1 1.833(3), Ru1–S1–C2 115.59(9), S1–Ru1–Cl1 165.87(2), P1–Ru1–P2

175.03(2), C1–Ru1–Cl2 174.40(8).

The formulations of complexes 9 (Fig. 3) and 10 (Fig. 4)

were confirmed by X-ray diﬀraction studies, however unequivo-

cal syntheses were not explored due to their rather mundane

nature.

The key bond lengths and angles of 9 and 10 are consistent

with other reported structures of thione bound N-methyl-2-

mercaptoimidazole ligands on Ru(^II) centres.^21,29For example,

the Ru–S bond lengths of 2.3845(6) Å in 9 and 2.4128(12),

2.4240(11) Å in 10 show little deviation from the range estab-

lished for published complexes (2.391–2.553 Å). Similarly, the

Ru1–S1–C2 angle of 115.59(9)° in 9 or 112.20(16) and 112.46

(14)° for 10 lie within the previously observed range 107–119°.

The molecular structure of 10 depicted in Fig. 4 is consistent

with spectroscopic data. The IR spectrum shows one CO

Fig. 4 Molecular structure of 10 in a crystal of 10·CHCl₃(hydrocarbon

hydrogen atoms and CHCl₃solvent omitted, phenyl groups simpliﬁed,

50% displacement ellipsoids). Selected bond lengths (Å) and angles (°):

Ru1–Cl1 2.4804(11), Ru1–Cl2 2.4763(11), Ru1–S1 2.4128(12), Ru1–S2

2.4240(11), Ru1–P1 2.3110(11), Ru1–C1 1.827(5), Ru1–S1–C11 112.20(16),

Ru1–S2–C15 112.46(14), S1–Ru1–S2 169.21(4), P1–Ru1–Cl2 175.58(4),

C1–Ru1–Cl1 170.99(14).

Scheme 3 Metallaboratrane degradation processes.

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absorption (1961 cm⁻¹) while the symmetric mutually trans

coordination of two methimazole groups was inferred through

¹H NMR integration relative to the triphenylphosphine co-

ligand. The triphenylphosphine ligand of isolated complex 10

gives rise to a resonance at δ_P= 45.1 and by a process of elim-

ination from the spectrum of the crude mixture, 9 was identi-

fied as being responsible for the resonance at δ_P= 19.1. The

formulations of both complexes were further confirmed by HR

ESI(+ve ion) mass spectrometry, with isotopic clusters corres-

ponding to [M − Cl]⁺at m/z = 803.0754 for 9 and 655.0102 for

10.

The platinaboratrane [Pt(PPh₃){κ⁴-B,S,S′,S″-B(mt)₃}](Pt→B)¹⁰

undergoes oxidative addition with Br₂or I₂to generate Pt(II)

complexes [PtX₂{κ⁴-B,S,S′,S″-B(mt)₃}](Pt→B)⁸(X = Br, I) with

retention of the Pt → B bond.²⁸In contrast, both the fer-

raboratrane [Fe(CO)₂{B(mt^tBu)₃}]²⁴and nickelaboratrane [NiBr

{B(mt^tBu)₃}]³⁰react with oxidants with rupture of the metal–

boron bond and formation of B-functionalised tris(mercapto-

imidazolyl)borate ligands. The reactions of 5 with either

elemental bromine or iodine proved to be complex (>10 pro-

ducts), with no single product predominating according to

spectroscopic analysis (³¹P NMR) of the crude reaction mixture

or samples subjected to fractional crystallisation. Group 8

(M → B)⁸metallaboratranes upon oxidative addition would be

expected to provide d⁶metal centres, i.e., devoid of a pair of

electrons housed in an orbital of metal–ligand σ-symmetry and

therefore unable to sustain a dative bond to boron. In the case

of Parkin’s (Fe → B)⁸system,²⁴which is able to presumably tra-

verse single-electron transfer radical pathways more easily

than ruthenium, addition of halogens across the Fe → B bond

is the preferred outcome. Owen’s report on the group 10

diptych metallaboratranes [M{BH(mp)₂}(PPh₃)] (M→B)¹⁰(M =

Pt, Pd; mp = 2-mercaptopyidyl), suggests a fine balance

between the coordination flexibility of the “BH(mp)₂” group.^11e

The “BH₂(mp)₂” unit typically coordinates facially, however in

these metallaboratranes the nearly trans-disposed sulfurs

exhibit more meridional-like κ³-B,S,S′ coordination (S–M–S =

161.14(3) Pt, 158.88(2)° Pd). Inspired by this result, 5 was

treated with hydride abstractor [CPh₃][PF₆] to assess the poten-

tial of 5 to relax to meridional coordination upon boron

hydride abstraction. Within two hours, the solution IR spec-

trum (THF) indicated a significant shift of the ν_COband from

1899 cm⁻¹in 5 to 1931 and 1972 cm⁻¹, consistent with the

conversion of a neutral to cationic complex. The conspicuous

absence of a BH stretching band was also noted in the IR spec-

trum. Both the ¹H and ³¹P{¹H} NMR spectra revealed broad

resonances. In the crude ³¹P{¹H} spectrum, the dominant

product was identified at δ_P= 39.6 accompanied with distinct

resonances corresponding to PF₆(δ_P= −142.9) and free PPh₃.

The broadness of the latter may imply the occurrence of rapid

exchange processes. The resonance at δ_P= 39.6 persisted fol-

lowing purification through washing with diethyl ether.

Attempts to identify the product through X-ray diﬀraction ana-

lysis of crystals obtained from slow evaporation of a benzene/

n-pentane solution aﬀorded the salt [RuF(Hmt)₂(CO)(PPh₃)₂]

PF₆[11]PF₆(Scheme 3, Fig. 5).

Fig. 5 Molecular structure of [11]⁺in a crystal of [11]PF₆·C₆H₆(benzene

solvent and counter anion omitted, aryl hydrogen atoms omitted,

phenyl groups simpliﬁed, 50% displacement ellipsoids). Selected bond

lengths (Å) and angles (°): Ru1–F1 2.098(2), Ru1–S1 2.4338(10), Ru1–S2

2.4238(11), Ru1–P1 2.3970(9), Ru1–P2 2.4277(10), Ru1–C1 1.818(4), F1–

Ru1–C1 177.70(15), S1–Ru1–F1 91.60(7), S2–Ru1–F1 92.30(7). Inset =

view normal to the P1–Ru1 vector illustrating bifurcated NH⋯F⋯HN

hydrogen bonding.

The cation of this salt features a terminal ruthenium fluoro

ligand, the coordination of which is stabilised by bifurcated

hydrogen bonding to two N–H groups from adjacent Hmt co-

ligands (NH⋯F = 1.627, 1.764 Å). The fluoride is coordinated

trans to the carbonyl ligand, as invariably observed for octa-

hedral ruthenium fluoro-carbonyl complexes, presumably to

maximise captodative interactions between the π-donor and

π-acidic characters of the two ligands. The Ru–F distance of

2.098(2) Å lies within the range established by simple octa-

hedral ruthenium complexes, despite the intramolecular

hydrogen bonding.³¹

In contrast to the analogous 1a which carries only one tri-

phenylphosphine, the two triphenylphosphines within

complex 5 each present potential sites for substitution and the

cis disposition of these results in some inter-ligand repulsion

which presumably also contributes to steric impetus in

addition to the now recognised trans influence of M → B inter-

actions. Accordingly, this aspect was investigated through

ligand substitution reactions. Facile and clean substitution of

triphenylphosphine was achieved by passing CO through a

solution of 5 in THF for 15 minutes to selectively yield the sym-

metrical cis-dicarbonyl complex [Ru(CO)₂(PPh₃){κ³-B,S,S′-BH

(mt)₂}] (12), with no evidence for the asymmetrical isomer 12x

(Scheme 4).

Scheme 4 Metallaboratrane carbonylation.

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The reaction proceeded with increased symmetry (C₁to C_s) regioselectivity. In addition, the introduction of π-acidic CO is

as inferred from the ¹H NMR spectrum, manifest by the re- electronically favourable in further relieving the electron

placement of the two distinct methyl resonances in 5 by one density at the π-basic electropositive Ru(0) metal centre.

resonance in 12 (δ_H= 3.43). The four independent olefinic Certainly, location of the two strongest π-acids (CO) trans to

proton resonances for 5 similarly simplified to two environ- the two strongest π-donors (mt) would be expected to maxi-

ments at δ_H= 6.62 and 6.69 [ABCD to AA′BB′]. The ¹³C{¹H} mise π-captodative eﬀects. The geometry of the ultimate

NMR spectrum contained fewer resonances, as expected for C_sproduct would seem kinetically counter-intuitive given the

12 compared to C₁5, in particular, the appearance of a single clear trans influence that is apparent in the molecular struc-

2

carbonyl resonance (δ_C= 202.9, d, J_CP= 2.4 Hz). Notably, only ture of 5. That said, it should be noted that a dissociative

one phosphine environment was present in the ³¹P{¹H} NMR pathway would involve a five-coordinate intermediate, the life-

spectrum of 12 (δ_P= 20.1), the broadness of which is consist- time of which may well be suﬃcient as to allow pseudo-rotation

ent with coordination trans to the boron. The spectrum to reposition the vacant site cis to the boron, i.e., the final

measured in situ included a resonance due to liberated PPh₃stereochemistry adopted need not necessarily reflect the site of

which was sharp, confirming that exchange with the co- initial dissociation. This is in contrast to substitution reactions

ordinated PPh₃did not occur on the ³¹P{¹H} NMR timescale of 1a wherein the triptych cage with more constrained geome-

(161 MHz at 25 °C). Furthermore, an absence of the resonance try is less able to undergo rearrangement. Additional details of

at δ_P= 52.7 corresponding to the phosphine of 5 trans to sulfur the molecular structure of 12 will be discussed collectively

suggested replacement at this position by the CO ligand. with further examples below.

Replacement of one phosphine by CO was further confirmed

by IR spectroscopy, which showed two ν_COassociated bands ing a crude sample of 12 to vacuum did not result in reforma-

(CH₂Cl₂: 1913, 1984 cm⁻¹).

tion of 5. The persistence of complex 12 was instead noted in

In contrast to the reversible CO coordination in 1a, subject-

1

The X-ray diﬀraction analysis of single crystals of 12·CHCl₃the H and ³¹P{¹H} NMR spectra, which suggested irreversible

shown in Fig. 6 was consistent with the symmetrical formu- coordination of the CO ligand. Together these observations

lation inferred from spectroscopic data. In contrast to 5, a suggest that coordination of CO trans to the Ru → B linkage is

space-filling diagram of 12 reveals less steric encumbrance less favourable than coordination trans to the π-basic thione

about the equatorial plane occupied by the two CO ligands. donors.

Nevertheless, it is noteworthy that the carbonyl ligands appear

Ligand exchange investigations were extended to consider a

to be displaced towards the Ru1–B1–H1 unit, a result that we range of electronically and sterically variant phosphines. The

attribute to an inter-ligand interaction in which this electron reaction of 5 with an excess of PMe₃proceeded cleanly within

rich group donates into the CO π* orbitals. The mitigation of one hour to give the product of mono-substitution [Ru(CO)

steric congestion associated with replacement at the equatorial (PMe₃)(PPh₃){BH(mt)₂}], the nature of which was inferred from

phosphine by CO is expected to be greater than at the (BRu) NMR spectroscopic data. The ³¹P{¹H} NMR spectrum revealed

axial position, which may provide a rationale for the observed the shift to higher frequency of both phosphine resonances

relative to 5, where the broad peak at δ_P= −29.6 suggests the

triphenylphosphine ligand was located trans to the boron, with

the doublet at δ_P= 58.7 (²J_PP= 11.3 Hz) corresponding to co-

ordinated PMe₃. Integration of the ³¹P{¹H} NMR resonances

confirmed the liberation of one triphenylphosphine. The

inferred product [Ru(CO)(PMe₃)(PPh₃){BH(mt)₂}], however,

eluded isolation, despite the promisingly clean NMR spectra

acquired for the crude reaction mixture. Failure to isolate the

product might reflect the lability and/or volatility of PMe₃.

Therefore, investigations were followed up with the less volatile

PMe₂Ph, which has electronic and steric properties not dissim-

ilar to PMe₃. As with the reactivity observed with PMe₃,

complex 5 was found to react with an excess of PMe₂Ph at

room temperature to aﬀord a single substitution product,

[Ru(CO)(PMe₂Ph)(PPh₃){BH(mt)₂}] 13 (Scheme 5).

Interestingly, substitution of the second phosphine was not

observed spectroscopically under these mild reaction con-

Fig. 6 Molecular structure of 12 in a crystal of 12·CHCl₃(aryl hydrogen

atoms and CHCl₃solvate omitted, phenyl groups simpliﬁed, 50% displa- ditions, despite the presence of excess PMe₂Ph. The spectro-

cement ellipsoids). Selected bond lengths (Å) and angles (°): B1–Ru1

2.237(2), B1–H1 1.03(4), Ru1–P1 2.4740(5), Ru1–C1 1.861(2), Ru1–C2

1.855(2), H1–B1–Ru1 117(2), B1–Ru1–P1 173.72(6), B1–Ru1–C1 82.18(9),

B1–Ru1–C2 81.16(9), C1–Ru1–C2 91.77(10). Insets = view along B1–Ru1

scopic data resemble those observed for the complex [Ru(CO)

(PMe₃)(PPh₃){BH(mt)₂}]. The broad resonance at δ_P= −17.2

was attributed to the PMe₂Ph ligand coordinated trans to the

Ru → B bond, while the relatively sharp doublet at δ_P= 56.9

(¹J_PC= 11.3 Hz) was assigned to the larger PPh₃ligand co-

vector and representation of angle (18.3°) between the S1–Ru1–S2 (red)

and C1–Ru1–C2 (blue) planes.

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18 hours (Scheme 5, Fig. 7). The formation of 14 was

accompanied by an increased complexity of the methyl region

(δ_H= 1.27–1.48, due to the presence of two chemically inequi-

valent PMe₂Ph ligands, each with a pair of diastereotopic P–

CH₃substituents with associated resonances each being doub-

lets, (two doublets would be expected for the C_sisomer of 14).

Four distinct P–CH₃resonances were also present in the ¹³C

{¹H} NMR spectrum of 14. Two of the PMe₂Ph methyl groups

couple to the chemically inequivalent phosphines in a doublet

1

3

of doublet multiplicity (δ_C= 15.6, J_CP= 31.2, J_CP= 3.3; 18.6,

¹J_CP= 32.3, J_CP= 4.2 Hz), while the other two P–CH₃reso-

nances appear only as doublets (δ_C= 16.3, J_CP= 13.6; 19.4,

3

1

¹J_CP= 16.2 Hz), presumably reflecting a Karplus-type C–P–Ru–

P dihedral angular dependence.³²Although rotation about the

Ru–P bond in solution is expected, the steric properties of the

phenyl moiety may well dictate conformational preferences.

Coordination of two PMe₂Ph ligands was further ascertained

by the respective sharp doublet and broad singlet phosphine

environments at δ_P= 14.5 (²J_PP= 12.3) and −16.4, respectively,

in the ³¹P{¹H} NMR spectrum.

By a process of elimination in the ¹H and ³¹P{¹H} NMR

spectra of resonances corresponding to 13 and 14, the third

product formed from the ambient temperature decomposition

Scheme 5 Phosphine substitution reactions of 5.

ordinated trans to one thione. The use of PMe₂Ph over the of 13 in CDCl₃is suggested to be the isomerised complex 13x

more symmetrical PMe₃is advantageous in that the two (Scheme 5). The methyl resonances in Fig. ESI-S1† consist of

methyl groups provide an indication of the local symmetry of two distinct doublets for the PMe₂Ph ligand (δ_H= 1.23, 1.45,

the complex. The asymmetric (C₁) nature of 13 was thus ²J_HP= 8.5 Hz), whereas the downfield resonances (δ_H= 3.19,

evident from ¹H NMR spectroscopy with the diastereotopic 3.24) correspond to the chemically inequivalent N-methyl

methyl groups of PMe₂Ph manifested as chemically inequiva- groups of the HB(mt)₂backbone coordinated to a C₁sym-

lent doublets at δ_H= 1.43 (¹J_HP= 5.3) and 1.28 (¹J_HP= 5.5 Hz); metric centre. The olefinic signals of all three products reside

1

whilst the remaining H signals show similarity to those of 5. in a similar chemical shift range of 6.40–6.58 ppm, which

Although crystals of 13 suitable for X-ray diﬀraction studies

were not obtained, the formulation of 13 was supported by the

identification of the [M + H]⁺peak at m/z = 769.1099 in the

ESI-MS.

The overnight acquisition of the ¹³C{¹H} NMR spectrum of

a pure sample of 13 revealed several (≈ 6) resonances in the

region typical of N-methyl mt substituents (δ_C= 33.5–34.2).

These appeared as distinct resonances in the ¹H NMR spec-

trum (measured after ¹³C data acquisition, see ESI Fig. S1†) at

δ_H= 3.44 and 3.48 (minor) and at δ_H= 3.30 and 3.35 (major).

The decomposition of 13 into these products occurred over

10 minutes from dissolution in CDCl₃, reaching equilibrium at

room temperature to provide a relative ratio of 2 : 3 : 5 for 13,

the minor product, and the major product. The formation of

these products was initially suspected to be due to the residual

acidity of the CDCl₃solvent. However, similar patterns

emerged when the less acidic CD₂Cl₂was used as the solvent.

To encourage conversion of 13 to the products previously

observed in CDCl₃, an aliquot of the crude reaction mixture of

13 in THF was briefly (≈ 2 minutes) heated to reflux. The NMR

Fig. 7 Molecular structure of 14 in a crystal of 14 (phenyl hydrogen

atoms omitted, phenyl groups simpliﬁed, 50% displacement ellipsoids).

Selected bond lengths (Å) and angles (°): B1–Ru1 2.253(4), B1–H1 1.09

(6), Ru1–P1 2.4095(9), Ru1–P2 2.2876(9), Ru1–C1 1.821(4), H1–B1–Ru1

spectra showed the clean partial conversion of 13 to complex

[Ru(CO)(PMe₂Ph)₂{BH(mt)₂}] (14), with no evidence for the

other decomposition product or the C_s-symmetric isomer of

14, which remains unknown. Full conversion of 13 to 14 was

120(3), B1–Ru1–P1 171.51(11), B1–Ru1–P2 88.00(11), B1–Ru1–C1 88.78

achieved on a preparative scale by heating in refluxing THF for (16), P1–Ru1–P2 99.57(3).

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occluded the identification of the resonances attributable to ordinated, which results in broadening for the former reso-

13x. The two dominant resonances in the ³¹P{¹H} NMR spec- nance. Meanwhile, the latter resonance for the equatorial

trum further support the assignment of 13x. Consistent with phosphite ligand remains unaﬀected, appearing as a sharp

the other ruthenaboratranes discussed herein, the two phos- doublet (²J_PP= 5.9 Hz).

phine associated resonances resolve as a broadened signal at

δ_P= 22.0 and a sharp doublet at δ_P= 12.9 (²J_PP= 11.4 Hz), PMe₃compared to P(OMe)₃is the ease of the second PPh₃sub-

which were assigned to PPh₃and PMe₂Ph, respectively. stitution. Single substitution predominately occurs with the

A notable diﬀerence in the reactivity of 5 with PMe₂Ph or

Compared to PMe₃and PMe₂Ph, trimethylphosphite has a electron rich alkyl phosphines at room temperature, and intro-

smaller steric profile and greater π-acidity. Treatment of 5 with duction of the second equivalent can be achieved only at elev-

a three-fold excess of P(OMe)₃for 18 hours at room tempera- ated temperatures. In contrast, substitution with P(OMe)₃

ture yielded the product of double substitution, the complex occurs readily at room temperature with replacement of both

[Ru(CO){P(OMe)₃}₂{BH(mt)₂}] 15. Whilst the crude ³¹P{¹H} triphenylphosphines. This is most likely a corollary of the

NMR spectrum revealed several (≈ 10) resonances, complex 15 greater capacity of π-acidic P(OMe)₃to stabilize the electron

was evident as the dominant species and could be purified rich Ru(0) centre cf. PPh₃. This is reflected by the IR shift to

through recrystallisation from diethyl ether and n-pentane. higher frequency from 1908 cm⁻¹in 5 to 1921 cm⁻¹in 15.

The formulation of 15 was established by NMR spectroscopy, Furthermore, replacement of the bulky PPh₃with P(OMe)₃is

mass spectrometry and a single crystal X-ray diﬀraction study sterically favourable (θ_T145° cf. 107°, respectively).

(Fig. 8).

Previous investigations on triptych ruthenaboratranes⁸

In addition to the characteristic resonances resulting from derived from 1a revealed that [Ru(CO)(PCy₃){B(mt)₃}] could not

1

the {BH(mt)₂} moiety in the H NMR spectrum, doublets at δ_Hbe isolated from the reaction of 1a with PCy₃because an equi-

= 3.67 (³J_HP= 11.1 Hz) and 3.56 (³J_HP= 10.8 Hz), are consistent librium between PPh₃and PCy₃coordination developed. An

with the coordination of two chemically inequivalent P(OMe)₃alternative approach utilised the complex [RuCl(Ph)(CO)

ligands. Given the electronegatively inductive (I⁻) eﬀects of the (PCy₃)₂] in a direct reaction with Na[HB(mt)₃] which obviated

methoxy substituents, the two P(OMe)₃resonances were the competitive presence of PPh₃. Similar synthetic strategies

observed as a doublet at δ_P= 151.1 (²J_PP= 19.4 Hz) and a broad were explored toward the complexes [Ru{BH(mt)₂}(CO)(PCy₃)

singlet at δ_P= 153.7, both as expected, downfield compared to (PPh₃)] and [Ru{BH(mt)₂}(CO)(PCy₃)₂] without success. It

complexes 5 and 12–14 of this series. The replacement of both should be noted that whilst the sterically congested cis-Ru

triphenylphosphine ligands in 5 by P(OMe)₃was further (PCy₃)₂fragment is understandably rare, it is not unknown.³³

demonstrated in the ¹³C{¹H} NMR spectrum by an absence of The room temperature reaction of 5 with two equivalents of

signals in the aromatic region and the appearance of two reso- PCy₃in THF for 20 hours yielded mainly starting material and

nances in the methoxy region (δ_C= 50.8, 52.0). The eﬀect of numerous minor products (∼10 resonances in the ³¹P{¹H}

the quadrupolar boron nuclei appears to extend to the methyl NMR spectrum). Heating under reflux for four hours facilitated

carbon resonance of the P(OMe)₃ligand to which it is trans co- further development of these resonances with the concurrent

appearance of free PPh₃and absence of the starting material.

However, the anticipated complex [Ru{BH(mt)₂}(CO)(PCy₃)

(PPh₃)] and other products could not be conclusively identi-

fied. Further attempts with a stoichiometric amount of PCy₃at

room temperature and at reflux, in Et₂O and THF, showed

either no reaction or produced ¹H and ³¹P{¹H} NMR spectra

that were similarly abundant in unidentifiable resonances. No

dynamic phosphine exchange was inferred from the sharp

resonance for the liberated PPh₃.

To eliminate possible complication of mixed PPh₃/PCy₃

coordination, the synthesis of the PCy₃analogue of 5 was

pursued through reaction of Na[H₂B(mt)₂] with [RuPhCl(CO)

(PCy₃)₂] in THF. The solution IR spectrum in THF of the crude

reaction mixture displays a CO band of low stretching fre-

quency 1898 cm⁻¹, amongst others (ν_CO= 1918, 1988 cm⁻¹).

This is indicative of ruthenium in the zero-oxidation state and

falls within the range 1877–1921 cm⁻¹established for the

ruthenaboratranes synthesised thus far and whilst these IR

Fig. 8 Molecular structure of 15 in a crystal (50% displacement ellip-

soids, one of three crystallographically distinct molecules shown).

Selected bond lengths (Å) and angles (°): B1–Ru1 2.252(3), B1–H1 1.17(5),

Ru1–P1 2.3604(8), Ru1–P2 2.2341(8), Ru1–C1 1.835(3), H1–B1–Ru1 122

data were promising, the presence of four sharp resonances of

equal intensity in the ³¹P{¹H} NMR spectrum suggested the

absence of phosphine coordination trans to the boron. Despite

numerous crystallisation experiments, only amorphous

powder unsuitable for X-ray diﬀraction studies was obtained.

(3), B1–Ru1–P1 173.33(9), B1–Ru1–P2 86.67(9), B1–Ru1–C1 81.66(13),

P1–Ru1–P2 99.56(3).

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The complications associated with the introduction of PCy₃^tBu, C₆H₂Me₃-2,4,6, C₆H₃Me₂-2,6).^1bWhilst 5 reacts readily

may be sterically and/or electronically disfavoured cf. PPh₃. with CN^tBu and CNC₆H₂Me₃-2,4,6 at room temperature, liber-

The steric bulk of the PCy₃ligand is considerably greater than ating free PPh₃, diﬃculties in purification precluded the iso-

that of PPh₃, and therefore it may be unfavourable to adja- lation of the desired products, [Ru{BH(mt)₂}(CO)(PPh₃)(CNR)]

cently accommodate two of these ligands around the ruthe- (R = ^tBu, C₆H₂Me₃-2,4,6). The infrared spectrum measured

nium centre. From the substitution reactions investigated thus within two hours of the reaction between 5 and CN^tBu in THF

far, the substitution process appears to be most facile and contained numerous overlapping peaks at 2109–2200 cm⁻¹, as

favoured for π-acidic ligands, such that the σ-basicity of the well as free CN^tBu (2070 cm⁻¹). The dominant bands at ν_CN

PCy₃ligand may disfavour its coordination to the electron rich 2134 and ν_CO= 1924 cm⁻¹may be evidence of the product of

Ru(0) centre.

mono-substitution, [Ru{BH(mt)₂}(CO)(PPh₃)(CN^tBu)]. Although

=

The replacement of both PPh₃ligands in 5 in the synthesis a stoichiometric amount of CNC₆H₂Me₃-2,4,6 was used in reac-

of complexes 14 and 15 led to the natural extension of the sub- tion with 5, incomplete reactivity was inferred by the presence

stitution reactivity to the inclusion of bidentate ligands. Given of free CNC₆H₂Me₃-2,4,6 (ν_CN= 2112 cm⁻¹) in the IR spectrum

the cis arrangement of the PPh₃ligands in 5, Z-1,2-bis(diphe- after an extended period (43 hours). Despite the plethora of

nylphosphino)ethylene (dppen), was envisaged as a suitable resonances (∼11) in the ³¹P{¹H} NMR spectrum, the IR spec-

bidentate ligand to ensure chelation, rather than formation of trum following recrystallisation from THF/n-pentane showed

bridged binuclear species as might be anticipated for the more evidence of the postulated product [Ru{BH(mt)₂}(CO)(PPh₃)

commonly employed 1,2-bis(diphenylphosphino)ethane (dppe) (CNMes)] with stretching frequencies of ν_BH= 2360, ν_CN

=

ligand. The conversion of

5

to [Ru{BH(mt)₂}(CO) 2088, and ν_CO= 1919 cm⁻¹, in a mixture with an unidentified

(Ph₂PCHvCHPPh₂)] 16 took place in THF under reflux for carbonyl containing complex at ν_CO= 1954 cm⁻¹, a value

43 hours, evident by the development of two downfield reso- inconsistent with zerovalent ruthenium. Neither fractional

2

nances at δ_P= 70.6 (d, J_PP= 8.1) and 50.8 (broad) in the ³¹P crystallisation nor column chromatography resulted in the iso-

{¹H} NMR spectra. The vinylic hydrogen resonances of the lation of a single pure material.

phosphine were obscured within the aromatic region but

Treatment of 5 with HC₅Me₆(HCp*) was envisaged as a

could be located from H¹³C HSQC experiments as multiplets potential alternative route to Goh’s borate complex [Cp*Ru

at δ_H= 7.91 and 7.97. The corresponding ¹³C{¹H} shifts appear (CO){κ²-S,S′-H₂B(mt)₂}],^19hwhich is akin to [Cp*Ru(CO){κ²-S,S′-

as two doublet of doublet resonances, respectively at δ_C= 148.1 H₂B(azain)₂}] (azain = 7-azaindolyl),³⁴thereby concomitantly

(¹J_CP= 26.6, ²J_CP= 26.6) and 149.0 (¹J_CP= 35.8, ²J_CP= 45.5). The probing phosphine substitution and Ru→B reactivity. No

C₁symmetry of 16 and the rigidity of the ethylene backbone reaction occurred at room temperature, while raising the temp-

renders each phenyl on the dppen chelate inequivalent. The erature to 80 °C resulted in a mixture of products. These

molecular structure of 16 was confirmed by an X-ray diﬀraction results perhaps unsurprisingly parallel those for HCuCPh and

1

study, as depicted in Fig. 9 and discussed below.

HBO₂C₆H₄discussed above in that the thermal conditions

The triptych ruthenaboratrane 1a undergoes clean and irre- required for the Ru→B bond to participate directly in reac-

versible substitution of the PPh₃ligand by isonitriles CNR (R = tions appear incompatible with the endurance of the resulting

products. This contrasts with the facile insertion of CS into a

Rh→B bond leading to the unusual thioketone complex [RhH

(PPh₃){η²-C,S:κ²-S′,S″-SC(PPh₃)BH(mt)₂}].¹⁴Treating 5 with CS₂

might have been expected to aﬀord the thiocarbonyl contain-

ing ruthenaboratrane [Ru(CS)(CO)(PPh₃){BH(mt)₂}], akin to

[Ru(CS)(PPh₃){B(mt)₃}],^1bhowever no reaction was observed at

room temperature, despite the phosphine lability demon-

strated above and the irreversible coordination of CS₂to other

zerovalent ruthenium centres established elsewhere.³⁵At

higher temperatures decomposition ensued with cleavage of

the borane ligand and formation of free methimazole.

Analysis and comparison of data

The series of complexes of the form [Ru(CO)(L¹)(L²){BH(mt)₂}]

synthesised from phosphine substitution reactions of 5 allow

an appraisal of the eﬀect of various co-ligands on the Ru → B

bond, in addition to a comparison with the triptych deriva-

tives, [Ru(CO)(L){B(mt)₃}].^1,8The key structural features of

Fig. 9 Molecular structure of 16 (aryl hydrogen atoms omitted, phenyl

groups simpliﬁed, displacement ellipsoids shown at 50%). Selected bond

lengths (Å) and angles (°): B1–Ru1 2.231(2), B1–H1 1.09(4), Ru1–P1

2.3636(5), Ru1–P2 2.2719(5), Ru1–C1 1.848(2), H1–B1–Ru1 121(2), B1–

complexes [Ru(CO)(L¹)(L²){BH(mt)₂}] (5, 12, 14, 15 and 16) and

[Ru(CO)(PPh₃){B(mt)₃}] (1a) are summarised in Table 1.

The [Ru(CO)(L¹)(L²){BH(mt)₂}] series is ordered in Table 1

Ru1–P1 175.39(6), B1–Ru1–P2 91.81(6), B1–Ru1–C1 86.26(9), P1–Ru1–

P2 85.29(2).

by increasing CO stretching frequency. This trend represents

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Table 1 Selected geometric and spectroscopic data for diptych ruthenaboratranes [Ru(CO)(L¹)(L²){BH(mt)₂}] (L²trans to boron)

L¹

L²

Ru → B [Å]

Ru–P(L¹) [Å]

Ru–P(L²) [Å]

δ_B[ppm]

ν_CO[cm⁻¹

]

PMe₂Ph

PPh₃

PMe₂Ph

PPh₃

2.253(4)

—

2.288(1)

—

2.3044(4)

2.2720(5)

2.2340(9)

—

2.4094(8)

—

5.00

5.13

4.12

5.05

3.80

2.97

17.1

1877

1890

1893

1905

1921

2.246(2)

2.231(1)

2.252(3)

2.237(2)

2.161(7)

2.4766(4)

2.3637(6)

2.3604(9)

2.4741(5)

2.435(1)

Ph₂PCHvCHPPh₂

P(OMe)₃

CO

P(OMe)₃

PPh₃

1913, 1984

1988

mt^a

—

^a[Ru(CO)(PPh₃){B(mt)₃}].^1,8

the relative decrease of electron density (π-basicity) of the tronic considerations. Notably, no viable correlation could be

ruthenium centres and parallels the progressive change of inferred between the elongated Ru–L₂bond and the Ru → B

electronic properties of the phosphine ligands from σ-basic bond distance.

PMe₂Ph to π-acidic P(OMe)₃. For the triptych analogues (ν_CO

=

Tricoordinate boranes are typically planar (∑°BX₃≈ 360°),

1871–1894 cm⁻¹),⁸this was shown to correlate well with with pyramidalisation of the boron attending interaction with

Tolman’s [Ni(CO)₃(L)]-derived electronic parameter³⁶and a a metal (M → BX₃; ideal tetrahedron (∑°BX₃≈ 328°). Thus,

similar trend is reproduced here and consistent with this the degree of pyramidalisation at the boron environment

observation, the ν_COstretching frequency of 14 is some might be used to estimate the strength of the Ru → B

44 cm⁻¹lower than 15. Whilst retrodonation to carbonyl bond.^7c,37Notwithstanding the usual caveats associated with

ligands involves metal orbitals of π-symmetry with respect to the precision of hydrogen atom positions in X-ray analysis, the

the M–L axes (‘t_2gtype’), retrodonation to boron involves a angle sum ∑°BX₃values of the complexes in the [Ru(CO)(L¹)

metal orbital of σ-symmetry (‘e_gtype’) such that variations in (L²){BH(mt)₂}] series span a comparatively narrow range of

one will only indirectly perturb the other. There is no absolute 317.5–326.1° bounded by 5 and 12 (Fig. 10).

correlation between Tolman’s electronic parameter and the Ru

A narrower range of 324.9–325.9° was established by the

→ B bond length, e.g., the two extremes of the series 14 (L¹= [Ru{B(mt)₃}CO(L)] series. The geometry around boron deviates

L²= PMe₂Ph) and 15 (L¹= L²= P(OMe)₃) have crystallograph- far from planarity in both series. This suggests a stronger M →

cally identical Ru–B bond lengths (2.253(4) and 2.252(3) Å, B interaction than in Bourissou’s Group 9, 10 and 11 metalla-

respectively). It should also be noted that the Tolman cone boratranes based on ambiphilic di- or tri-phosphino borane

angles for these two comparatively compact ligands are not so ligands adopting larger (i.e., more trigonal) ∑°BX₃values (e.g.,

dissimilar (122 cf. 107°). The shortest Ru → B bond length is Group 10, M → B: 341.8–336.7).^7c,36The variation of pyramida-

observed for the dppen derivative 16 (2.231(1) Å) however that lisation is most remarkable between 5 and 12 where the

is perhaps to be expected given that the dppen chelate sub- smaller ∑°BX₃value (greater pyramidalisation) of the former

tends an acute bite angle (85.29(2)°) whilst in all other cases may result from the greater steric imposition of PPh₃on the

the L¹–Ru–L²angle between donor atoms is obtuse. It must be

stressed that for this series of similar complexes, the range of

Ru → B bond lengths spans only some 22 pm whilst the pre-

cision for comparison of bond lengths (6 × e.s.d.) spans 6–24

pm, due in part to the caveats associated with locating com-

paratively light atoms such as boron, adjacent to heavy metal

atoms, i.e., this geometric parameter is not likely to be reliably

informative. Indirect insights into the impact of Ru → B

bonding are, however, provided by the more precisely deter-

mined Ru–P bond lengths. In every case where two phosphines

are present, the Ru–P bond length trans to the Ru → B bond is

very significantly longer than that trans to the thione, by as

much as 0.058 Å in the case of 5. However, it should be noted

that whilst 5 has the greatest disparity, this should not be

attributed to the Ru–B trans influence alone, since of all the

phosphines employed, PPh₃has the largest Tolman cone

angle, i.e., there will be a steric as well as electronic com-

ponent operating. The diﬀerence in bond lengths was found to

Fig. 10 Lack of relationship between the Ru → B distance and the pyra-

be least pronounced for complex 16 with the bidentate dppen

ligand, which may reflect the constraints of chelation over elec- L₂{BH(mt)₂}] (blue) and [Ru(CO)L{B(mt)₃}]⁸(red).

midalization sum around the boron (∑°BX₃) for complexes [Ru(CO)

Dalton Trans.

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Scheme 6 Regioselectivity of ligand substitution in diptych

ruthenaboratranes.

Fig. 11 Correlation between the pyramidalization at boron and the

Tolman steric parameter,³⁵θ_T, for the complexes [Ru(CO)L₂{BH(mt)₂}].

or Bailar twist mechanisms.³⁸We have previously observed

such a process to occur upon heating octahedral cationic trip-

tych rhodaboratranes²²and Ball and Mann have provided

NMR-derived evidence for [RuH₂(CO)(PPh₃)₃] undergoing

intramolecular phosphine site exchange upon heating.^38e

Given the mild conditions employed herein, we remain dis-

posed towards the 5-coordinate pseudo-rotation interpretation.

It should however be noted in this context that 5-coordinate

rhodaboratranes have been isolated in which the ground

state has the contrary geometry with a vacant site trans to

the Rh→B bond, e.g., Bourissou’s 2-phosphinoaryl borane

archetype [RhCl(DMAP){BPh(C₆H₄PⁱPr₂-2)₂}],^7athe preference

for reduced coordination numbers for group 9 (cf. group 8)

notwithstanding.

boron environment than CO. Indeed, whilst there is no

obvious correlation between the degree of pyramidalization

and associated Ru → B bond length (Fig. 10), there is a mono-

tonic relationship between pyramidalization and the Tolman

steric parameter (θ_T, Fig. 11), notwithstanding the uncertain-

ties of defining such a parameter for CO (95°)³⁶and for chelat-

ing dppen, which we have approximated to PMePh₂. This

somewhat over-estimates the steric profile of each half of the

dppen ligand given the constraints of chelation and the associ-

ated preclusion of free rotation around the metal–phosphorus

bond, an assumption upon which the Tolman parameter is

based. Thus there is most likely even better correlation than

might be suggested by the approximation to PMePh₂. Thus

deformation of the boron coordination sphere, appears to be a

plausible response to steric congestion that need not signifi-

cantly compromise Ru → B binding.

The peculiarities of the coordination chemistry of Z-type

(i.e., σ-Lewis acidic) ligands³⁹in contrast to more classical elec-

tron-pair donor ligands (X, L) would seem to call for further

study.

Conclusions

The syntheses of diptych ruthenaboratranes have been devel-

oped, with the first example [Ru(CO)(PPh₃)₂{BH(mt)₂}] (5) pro-

viding access to further examples via mono or disubstitution

Experimental

General consideration

of the PPh₃ligands. Whilst extensive structural data attest to a All manipulations were carried out under a dry and oxygen-

significant trans influence on the part of the Ru → B bond, the free nitrogen atmosphere using standard Schlenk vacuum line,

trans eﬀect is somewhat more subtle in that the kinetic pro- and inert atmosphere dry-box techniques, with dried and

ducts of monosubstitution (12, 13) have the extraneous ligand degassed solvents that were distilled from either calcium

positioned cis to the Ru → B bond. We attribute this to the geo- hydride (CH₂Cl₂) or sodium and benzophenone (ethers,

metric flexibility of the 5-coordinate intermediate arising from hexane, THF, toluene, xylene and paraﬃns). NMR spectra were

initial PPh₃dissociation, with rearrangement to present the obtained at 298 K on a Varian Mercury 300 (¹H: 300.1 MHz,

vacant coordination site in the cis position rather than trans to ³¹P: 121.5 MHz), a MR 400 (¹H: 399.8 MHz, ³¹P: 161.8 MHz), a

the Ru → B bond. Implicit in this interpretation is the reluc- Bruker Avance 400 (¹H: 400.1 MHz, ¹¹B: 128.4 MHz, ¹³C:

tance of CO to assume the position trans to the Ru–B bond 100.6 MHz, ³¹P: 162.0 MHz), a Bruker Avance 600 (¹H:

rather than the more σ-basic phosphorus ligands, which 600.0 MHz, ¹³C: 150.9 MHz), or a Bruker Avance 700 (¹H:

would also tally with the lability of the CO ligand observed in 700.2 MHz, ¹³C: 176.1 MHz, ³¹P: 283.5 MHz). ¹H chemical

the triptych system for [Ru(CO)₂{B(mt)₃}] (Scheme 6).^1bWe are shift (δ) data were referenced to residual solvent peaks in

unable at this stage to discount arrival at the thermodynamic deuterated solvent. ¹³C chemical shift (δ) data were referenced

isomer via an initially formed kinetic isomer that undergoes a to the resonances of the deuterated solvent. ³¹P and ¹¹B were

subsequent non-dissociative isomerism such as the Ray–Dutt referenced to external 85% H₃PO₄or BF₃·OEt₂standards,

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Dalton Transactions

respectively. Infrared spectra were obtained with a Bruker ³¹P{¹H} NMR (162 MHz, CDCl₃): δ_P= 52.7 (s.br., PPh₃trans to

2

Alpha FTIR with diamond plate Attenuated Total Reflectance S), 19.3 (s.br., PPh₃trans to B, J_PPnot resolved). ¹¹B{¹H} NMR

sampling attachment, run at 4 cm⁻¹resolution. Solution infra- (128 MHz, CDCl₃): δ_B= 4.12 (s.br.). ¹¹B NMR (128 MHz,

1

red spectra were obtained using a PerkinElmer Spectrum One CDCl₃): δ_B= 3.81 (s.br., J_BHnot resolved). ESI-MS(+) m/z =

FT-IR Spectrometer. Elemental microanalysis was performed 895.2 [M − CO + OMe]⁺. Accurate mass: Found 895.1592 [M −

by the London Metropolitan University. Electrospray (ESI) CO + OMe]⁺, Calcd for C₄₅H₄₄¹¹BN₄OP₂¹⁰²RuS₂: 895.1568.

mass spectrometry were performed by the Research School of Anal. Found: C, 60.52; H, 4.77; N, 6.13%. Calcd for

Chemistry mass spectrometry service. Data for X-ray crystallo- C₄₅H₄₁BN₄OP₂RuS₂: C, 60.61; H, 4.63; N, 6.28%. Crystal data

graphy were collected with an Agilent SupaNova diﬀract- for C₄₅H₄₁BN₄OP₂RuS₂·C₄H₁₀O at 185 K: M_w= 965.93, monocli-

ometer. The complexes [RuCl(Ph)(CO)(PPh₃)₂]¹⁵and [RuCl nic, P2₁/n, a = 12.2007(3) Å, b = 24.2676(5) Å, c = 15.8232(3) Å,

(CHvCHPh)(CO)(PPh₃)₂]¹⁶and the pro-ligand salt Na[H₂B β = 99.4773(19)°, V = 4621.02(9) Å³, Z = 4, D_calcd= 1.388 Mg

(mt)₂]¹⁷were prepared as described previously. Other reagents m⁻³, μ(Mo Kα) = 0.54 mm⁻¹, T = 185(2) K, clear pale yellow

were used as received from commercial suppliers.

block, 0.14 × 0.10 × 0.06 mm, 10 695 independent reflections.

F²refinement, R₁= 0.037, wR₂= 0.070 for 8455 reflections (I >

2.0σ(I), 2θ_max= 60°), 553 parameters, 0 restraints. Crystal data

Synthesis of [Ru(CO)(PPh₃)₂{BH(mt)₂}](Ru→B)⁸(5)

Method 1: A suspension of [RuCl(Ph)(CO)(PPh₃)₂] (0.500 g, for C₄₅H₄₁BN₄OP₂RuS₂·C₄H₁₀O: M_w= 965.93, monoclinic, P2₁/

0.65 mmol) and Na[H₂B(mt)₂] (0.175, 0.67 mmol) in diethyl n, a = 12.2141(1) Å, b = 24.2890(2) Å, c = 15.8351(1) Å, β =

ether (50 mL) was stirred for 15 h, by which time the suspen- 99.4996(7)°, V = 4633.35 (3) Å³, Z = 4, D_calcd= 1.385 Mg m⁻³

,

sion had lightened from an orange colour to beige. The μ(Cu Kα) = 4.57 mm⁻¹, T = 150(2) K, clear pale yellow block,

solvent was removed in vacuo and the resulting residue was re- 0.12 × 0.08 × 0.08 mm, 9370 independent reflections. F²refine-

dissolved in dichloromethane (30 mL). The filtrate was trans- ment, R₁= 0.023, wR₂= 0.058 for 9370 reflections (I > 2.0σ(I),

ferred to another Schlenk flask by cannula filtration. An equal 2θ_max= 144°), 553 parameters, 0 restraints CCDC 1881115.†

volume of ethanol was added, and the solvent was removed Crystal data for [Ru(Ph)(κ²-N,S-mt)(CO)(PPh₃)₂] (6), see also ref.

slowly under reduced pressure to aﬀord a beige precipitate 21. C₄₇H₄₀N₂OP₂RuS: M_w= 843.93, monoclinic, P2₁/n, a =

that was filtered and dried under high vacuum. Yield: 0.198 g 13.1748(1) Å, b = 18.1695(1) Å, c = 17.5732(1) Å, β = 110.7668

(0.222 mmol, 34%).

(8)°, V = 3933.36(2) Å³, Z = 4, D_calcd= 1.425 Mg m⁻³, μ(Cu Kα) =

Method 2: A suspension of [RuHCl(CO)(PPh₃)₃] (1.000 g, 4.79 mm⁻¹, T = 150(2) K, clear light yellow needle, 0.22 × 0.05

1.05 mmol) and ethynylbenzene (0.30 mL, 2.7 mmol, excess) × 0.04 mm, 7972 independent reflections. F²refinement, R₁=

in dichloromethane (35 mL) was stirred for 1.5 h, by which 0.024, wR₂= 0.062 for 7260 reflections (I > 2.0σ(I), 2θ_max= 60°),

time the solution had turned to a deep red colour at which 487 parameters, 0 restraints, CCDC 1881156.† Crystal data

point Na[H₂B(mt)₂] (0.275 g, 1.05 mmol) was added. The reac- for [Ru(CuCPh)(CO)(PPh₃){H₂B(mt)₂}] (8) C₃₅H₃₂BN₄OPRuS₂-

ˉ

tion mixture was stirred for a further 18 h, and the filtrate iso- CHCl₃: M_w= 850.98, triclinic, P1 (no. 2), a = 9.9810(7) Å,

lated by cannula filtration. The solvent was concentrated b = 11.0018(6) Å, c = 19.3279(8) Å, α = 73.725(4)°, β =

in vacuo to ≈5 mL. Diethyl ether (20 mL) was added to the 82.147(4)°, γ = 65.670(6)°, V = 1855.8(2) Å³, Z = 2, D_calcd= 1.523

yellow oily residue, to aﬀord a pale yellow solid that was iso- Mg m⁻³, μ(Cu Kα) = 7.15 mm⁻¹, T = 150(2) K, yellow prism,

lated by cannula filtration. Petroleum ether was added and the 0.11 × 0.08 × 0.04 mm, 7474 independent reflections. F²refine-

solid collected on a sintered funnel, washed with diethyl ether ment, R₁= 0.032, wR₂= 0.083 for 6775 reflections (I > 2.0σ(I),

and petroleum ether, then dried under high vacuum. Yield: 2θ_max= 144°), 450 parameters, 0 restraints, CCDC 1881116.†

0.570 g (0.639 mmol, 61%). Crystals of a diethyl ether solvate

Reaction of [Ru(CO)(PPh₃)₂{BH(mt)₂}] with HCl

suitable for crystallographic analysis were obtained from slow

evaporation of a concentrated solution of 5 in diethyl ether An ethereal solution of hydrogen chloride (0.25 mL, 1 M,

over one day. IR (ATR, cm⁻¹): 2316 ν_BH, 1893 ν_CO. IR (CH₂Cl₂): 0.25 mmol) was added to a stirred solution of [Ru(CO)

2397 ν_BH, 1899 ν_CO. ¹H NMR (400 MHz, CDCl₃): δ_H= 3.07, 3.33 (PPh₃)₂{BH(mt)₂}] (5: 0.200 g, 0.22 mmol) in tetrahydrofuran

(s × 2, 3 H × 2, CH₃), 4.07 (s, v.br., 1 H, BH), 6.04 (d, 1 H, and the mixture was stirred for 24 h. The ³¹P{¹H} NMR spec-

3

³J_HH= 1.8, NCHvCH), 6.15 (d, 1 H, J_HH= 1.8, NCHvCH), trum revealed a mixture of products at δ_P= 55.2, 50.0, 45.2,

3

6.50 (d, ¹H, J_HH= 1.7, NCHvCH), 6.58 (d, 1 H, J_HH= 1.8, 35.7, 28.1 and 19.1 in addition to free triphenylphosphine.

NCHvCH), 6.97–7.07 (m, 9 H, C₆H₅), 7.22–7.26 (m, 9 H, The solvent was removed using a rotary evaporator and the

C₆H₅), 7.40–7.47 (m, 12 H, C₆H₅). ¹³C{¹H} NMR (176 MHz, orange residue was crystallized from chloroform and

CDCl₃): δ_C= 33.7, 34.1 (CH₃× 2), 119.8 (NCHvCH), 120.3 n-pentane. The crystals were collected on a sintered frit and

(NCHvCH), 120.7 (NCHvCH), 120.9 (NCHvCH), 126.4 [d, dried in air to give a mixture of the products below. Combined

2,3

J

CP

= 8.8, C^2,3,5,6(C₆H₅)], 127.5 [br, C^2,3,5,6(C₆H₅) for PPh₃yield: 0.073 g.

trans to B], 128.1 [d, J_CP= 1.8, C⁴(C₆H₅)], 128.5 [C4(C₆H₅) for

PPh₃trans to B], 134.3 [d,

Product 1: [RuCl₂(CO)(PPh₃)₂(Hmt)] (9): ESI-MS(+) m/z: 803.1

4

2,3

J

= 14.1, C^2,3,5,6(C₆H₅) for PPh₃[M − Cl]⁺, 844.1 [M − Cl + MeCN]⁺. Accurate mass: Found

CP

2,3

1

trans to B], 134.5 [d,

J

CP

= 8.8, C^2,3,5,6(C₆H₅)], 137.1 [d, J_CP

=

803.0754 [M −

Cl]⁺, Calcd for C₄₁H₃₆N₂O³⁵Cl₂P₂S¹⁰²Ru:

19.4, C¹(C₆H₅) for PPh₃trans to B], 137.9 [d, J_CP= 40.5, 803.0750; Found 844.1021 [M − Cl + MeCN]⁺, Calcd for

1

C¹(C₆H₅)], 163.6, 164.8 (CS × 2), 208.5 (d, J_CP= 15.6, CO). C₄₃H₃₉N₃O³⁵ClP₂S¹⁰²Ru:

844.1016.

Crystal

data

for

2

Dalton Trans.

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C₄₁H₃₆Cl₂N₂OP₂RuS·CHCl₃: M_w= 958.11, monoclinic, P2₁/c, a μ(Cu Kα) = 8.24 mm⁻¹, T = 150(2) K, yellow trapezoid, 0.31 ×

= 11.5279(1), b = 20.9802(1), c = 18.3591(2) Å, V = 4222.02(5) Å³, 0.25 × 0.16 mm, 6486 independent reflections. F²refinement,

Z = 4, D_calcd= 1.507 Mg m⁻³, μ(Cu Kα) = 7.38 mm⁻¹, T = 150(2) R₁= 0.029, wR₂= 0.078 for 7799 reflections (I > 2.0σ(I), 2θ_max

K, orange needle, 0.18 × 0.05 × 0.05 mm, 8525 independent 144°), 391 parameters, 0 restraints, CCDC 1881122.†

reflections. F²refinement, R₁= 0.031, wR₂= 0.078 for 7799

=

Synthesis of [Ru(CO)(PMe₂Ph)(PPh₃){BH(mt)₂}] (Ru→B)⁸(13)

reflections (I > 2.0σ(I), 2θ_max= 144°), 490 parameters, 0

restraints, CCDC 1881118.†

A solution of [Ru(CO)(PPh₃)₂{BH(mt)₂}] (5: 0.203 g, 0.23 mmol)

Product 2: [RuCl₂(CO)(PPh₃)(Hmt)₂] (10): washing the iso- and PMe₂Ph (0.10 mL, 0.70 mmol) in tetrahydrofuran (20 mL)

lated mixture with chloroform and filtering under vacuum was stirred for 4 h. The solvent was removed in vacuo to give an

suction aﬀorded a second product. IR (ATR, cm⁻¹): 3028 ν_CH

,

oily orange residue. Diethyl ether (20 mL) was added to aﬀord

1

1961 ν_CO. H NMR (400 MHz, CDCl₃): δ_H= 3.42 (s, 6 H, CH₃), a pale yellow solid that was isolated by cannula filtration. The

3

6.61 (t, 2 H, J_HH= 2.3, NCHvCH), 6.75 (t, 2 H, J_HH= 2.4, solid was suspended in n-pentane and collected on a sinter

NCHvCH), 7.30–7.33 (m, 9 H, C₆H₅), 7.79–7.82 (m, 6 H, funnel, washed with n-pentane, then dried under high

C₆H₅), 12.92 (s.br., 2 H, NH). ¹³C{¹H} NMR (100 MHz, CDCl₃): vacuum. Yield: 0.059 g (0.077 mmol, 34%). IR (ATR, cm⁻¹):

δ_C= 34.2 (CH3), 115.2 (NCHvCH), 119.5 (NCHvCH), 127.6 [d, 3044 ν_CH, 2363 ν_BH, 1890 ν_CO. IR (THF, cm⁻¹): 2337 ν_BH, 1902

2,3

4

1

2

J

CP

= 10.0, C^2,3,5,6(C₆H₅)], 129.7 [d, J_CP= 3.0, C⁴(C₆H₅)], ν_CO. H NMR (400 MHz, CDCl₃): δ_H= 1.28 (d, 3 H, J_HP= 5.5,

133.8 [d, J_CP= 48.3, C¹(C₆H₅)], 134.5 [d,

J

CP

= 9.1, PCH₃), 1.43 (d, 3 H, ²J_HP= 5.3, PCH₃), 3.00 (s, 3 H, NCH₃), 3.43

1

2,3

C^2,3,5,6(C₆H₅)], 158.1 (CS). ³¹P{¹H} NMR (162 MHz, CDCl₃): δ_P= (s, 3 H, NCH₃), 6.19 (d, 2 H, J_HH= 2.6, NCHvCH), 6.60 (s,

3

45.1. ESI-MS(+) m/z: 689.1 [M − H]⁺, 655.0 [M − Cl]⁺. Accurate 2 H, NCHvCH), 7.07–7.13 (m, 9 H, C₆H₅), 7.30–7.52 (m, 14 H,

mass:

Found

655.0102

[M

−

Cl]⁺,

Calcd

data

for C₆H₅). Decomposition in CDCl₃confounded the acquirement

C₂₇H₂₇N₄O³⁵ClPS₂¹⁰²Ru:

655.0104.

Crystal

for of useful ¹³C{¹H} NMR data. ³¹P{¹H} NMR (162 MHz, CDCl₃):

C₂₇H₂₇Cl₂N₄OPRuS₂: M_w= 690.58, monoclinic, Cc, a = 9.2352 δ_P= 56.9 (d, J_PC= 11.3, PPh₃), −17.2 (s.br., PMe₂Ph). ¹¹B{¹H}

1

(4), b = 16.5996(6), c = 18.7713(7) Å, β = 94.733(4)°, V = 2867.84 NMR (128 MHz, CDCl₃): δ_B= 5.13 (s.br.). H NMR (400 MHz,

(19) Å³, Z = 4, D_calcd= 1.599 Mg m⁻³, μ(Mo Kα) = 0.96 mm⁻¹, T CD₂Cl₂): δ_H= 1.25 (d, 3 H, J_HP= 5.5, PCH₃), 1.38 (d, 3 H,

2

= 150(2) K, yellow block, 0.18 × 0.12 × 0.06 mm, 5442 indepen- ²J_HP= 5.3, PCH₃), 2.97 (s, 3 H, NCH₃), 3.49 (s, 3 H, NCH₃), 6.19

dent reflections. F²refinement, R₁= 0.029, wR₂= 0.065 for (d, 1 H, J_HH= 1.4, NCHvCH), 6.27 (s, 1 H, NCHvCH), 6.63

3

5212 reflections (I > 2.0σ(I), 2θ_max= 144°), 345 parameters, 2 (d, 1 H, J_HH= 1.5, NCHvCH), 6.67 (s, 1 H, NCHvCH),

restraints, CCDC 1881117.†

7.07–7.16 (m, 9 H, C₆H₅), 7.31–7.48 (m, 14 H, C₆H₅). ³¹P{¹H}

NMR (162 MHz, CD₂Cl₂): δ_P= 56.2 (s.br., PMe₂Ph), −17.7 (s.

br., PPh₃). ESI-MS(+) m/z: 769.1 [M + H]⁺. Accurate mass:

Synthesis of [Ru{BH(mt)₂}(CO)₂(PPh₃)] (Ru→B)⁸(12)

Carbon monoxide (1 atm) was bubbled through a stirred solu- Found 769.1099 [M + H]⁺, Calcd for C₃₅H₃₈ON₄¹¹BP₂S₂¹⁰²Ru

tion of [Ru(CO)(PPh₃)₂{BH(mt)₂}] (5: 0.205 g, 0.23 mmol) in di- 769.1093. Anal. Found: C, 55.29; H, 5.02; N, 7.13%. Calcd for

chloromethane for 15 min. The solvent was removed in vacuo C₃₅H₃₇BN₄OP₂RuS₂: C, 54.76; H, 4.86; N, 7.30%.

to give a yellow residue, which was then suspended in diethyl

Synthesis of [Ru(CO)(PMe₂Ph)₂{BH(mt)₂}] (Ru→B)⁸(14)

ether (10 mL). The yellow solid was isolated by cannula fil-

tration, washed with n-pentane (20 mL) and dried under A solution of [Ru(CO)(PPh₃)₂{BH(mt)₂}] (5: 0.200 g, 0.22 mmol)

vacuum. Yield: 0.079 g (0.120 mmol, 52%). Crystals of a chloro- and PMe₂Ph (0.30 mL, 2.7 mmol) in tetrahydrofuran (20 mL)

form solvate 12·CHCl₃suitable for crystallographic analysis was heated under reflux for 18 h. The solvent was reduced to

were obtained from slow evaporation of a concentrated solu- 3 mL and diethyl ether (10 mL) and n-pentane (15 mL) were

tion of 12 in chloroform/n-pentane over one day. IR (ATR, added to aﬀord a pale yellow solid that was isolated by

1

cm⁻¹): 2344 ν_BH, 1984, 1913 ν_CO. H NMR (700 MHz, CDCl₃): cannula filtration and dried under high vacuum. Yield: 0.079 g

δ_H= 3.43 (s, 6 H, CH₃), 6.62 (s, 2 H, NCHvCH), 6.69 (s, 2 H, (0.12 mmol, 55%). Crystals suitable for crystallographic ana-

NCHvCH), 7.36–7.39 (m, 9 H, C₆H₅), 7.52–7.55 (m, 6H, C₆H₅). lysis were obtained from slow evaporation of a concentrated

¹³C{¹H} NMR (176 MHz, CDCl₃): δC = 34.4 (CH₃), 120.9 solution of 14 in tetrahydrofuran/diethyl ether/n-pentane over

2,3

(NCHvCH), 122.1 (NCHvCH), 128.3 [d,

J

CP

=

8.8, one day. IR (ATR, cm⁻¹): 2298 ν_BH, 1877 ν_CO. IR (THF, cm⁻¹):

C^2,3,5,6(C₆H₅)], 129.4 [d, J_CP= 1.2, C⁴(C₆H₅)], 133.6 [d,

J

=

2323 ν_BH, 1902 ν_CO. H NMR (700 MHz, CDCl₃): δ_H= 1.27 (d,

4

2,3

1

CP

13.2, C^2,3,5,6(C₆H₅)], 136.3 [d, J_CP= 27.1, C¹(C₆H₅)], 163.9 (d, 3 H, J_HP= 8.6, PCH₃), 1.38 (d, 3 H, J_HP= 5.0, PCH₃), 1.43 (d,

1

2

³J_CP= 20.2, CS), 202.9 (d, J_CP= 2.4, CO). ³¹P{¹H} NMR 3 H, J_HP= 5.4, PCH₃), 1.48 (d, 3 H, J_HP= 8.4, PCH₃), 3.40 (s,

2

(162 MHz, CDCl₃): δ_P= 20.1. ¹¹B NMR (128 MHz, CDCl₃): δ_B

=

3 H, NCH₃), 3.44 (s, 3 H, NCH₃), 6.48 (d, 1 H, J_HH= 1.6,

3

2.97 (s.br.). ESI-MS(+) m/z: 648.1 [M − B]⁺, 659.0 [M + H]⁺. NCHvCH), 6.53 (s, 1 H, NCHvCH), 6.58 (s, 1 H, NCHvCH),

3

Accurate mass: Found 659.0441 [M

+

H]⁺, Calcd for 6.65 (d, 1 H, J_HH= 1.7, NCHvCH), 7.09–7.13 (m, 3 H, C₆H₅),

C₂₈H₂₇¹¹BN₄O₂PS₂¹⁰²Ru: 659.0450. Anal. Found: C, 51.29; H, 7.20–7.22 (m, 2 H, C₆H₅), 7.26–7.28 (m, 1 H, C₆H₅), 7.31–7.33

3.95; N, 8.37%. Calcd for C₂₈H₂₆BN₄O₂PRuS₂: C, 51.15; H, (m, 2 H, C₆H₅), 7.43–7.46 (m, 2 H, C₆H₅). ¹³C{¹H} NMR

1

3

3.99; N, 8.52%. Crystal data for C₂₈H₂₆BN₄O₂PRuS₂·CHCl₃: M_w(176 MHz, CDCl₃): δ_C= 15.6 (dd, J_CP= 31.2, J_CP= 3.3, PCH₃),

1

3

= 776.90, monoclinic, P2₁/c, a = 9.7228(1), b = 18.6012(1), c = 16.3 (d, J_CP= 13.6, PCH₃), 18.6 (dd, J_CP= 32.3, J_CP= 4.2,

17.8876(1) Å, V = 3205.42(2) Å³, Z = 4, D_calcd= 1.610 Mg m⁻³

,

PCH₃), 19.4 (d, J_CP= 16.2, PCH₃), 34.1 (NCH₃), 34.1 (NCH₃),

1

Dalton Trans.

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Paper

Dalton Transactions

4

120.6 (d, J_CP= 8.4, NCHvCH) overlapping with 120.6 (d, J_CP92.0931(12)°, γ = 93.9263(13)°, V = 3792.32(6) Å³, Z = 2, D_calcd

=

= 7.6, NCHvCH), 121.1 (NCHvCH), 121.5 (NCHvCH), 127.3 1.617 Mg m⁻³, μ(Cu Kα) = 8.14 mm⁻¹, T = 150(2) K, colourless

2,3

[d,

J

=

8.2, C^2,3,5,6(C₆H₅)], 128.0 [d,

J

CP

= 7.7, needles, 0.42 × 0.06 × 0.04 mm, 15 286 independent reflec-

CP

C^2,3,5,6(C₆H₅)], 127.6 [C⁴(C₆H₅)], 127.8 [C⁴(C₆H₅)], 129.3 [d, tions. F²refinement, R₁= 0.038, wR₂= 0.098 for 13 859 reflec-

2,3

J

CP

= 7.8, C^2,3,5,6(C₆H₅)], 129.7 [d, ^2,3J_CP= 11.4, C^2,3,5,6(C₆H₅)], tions (I > 2.0σ(I), 2θ_max= 144°), 914 parameters, 0 restraints,

143.2 [dd, J_CP= 35.1, J_CP= 5.9, C¹(C₆H₅)], 143.3 [d, J_CP

=

CCDC 1881124.†

1

3

1

20.7, C¹(C₆H₅)], 165.0 (d, J_CP= 23.7, CS), 165.3 (d, J_CP= 20.2,

3

2

Synthesis of [Ru(CO)(Z-Ph₂PCHvCHPPh₂){BH(mt)₂}]

(Ru→B)⁸(16)

CS), 207.7 (dd, J_CP= 15.5, J_CP= 3.3, CO). ³¹P NMR (283 MHz,

CDCl₃): δ_P= 14.5 (m.br., coupling not resolved, PMe₂Ph trans

to S), −16.4 (s.br., PMe₂Ph trans to B). ³¹P{¹H} NMR (283 MHz, A solution of [Ru(CO)(PPh₃)₂{BH(mt)₂}] (5: 0.200 g, 0.22 mmol)

1

CDCl₃): δ_P= 14.5 (d, J_PC= 12.3, PMe₂Ph trans to S), −16.4 (s. and Z-PPh₂CHvCHPPh₂(0.090 g, 0.22 mmol) in tetrahydro-

br., PMe₂Ph trans to B). ¹¹B NMR (128 MHz, CDCl₃): δB = furan (20 mL) was heated under reflux for 43 h. The solvent

5.00 (s.br.). ESI-MS(+) m/z: 633.0 [M

mass: Found 1311.1317 [2

Na]⁺, Calcd for orange residue to give a yellow solid that was isolated by

−

B]⁺. Accurate was removed in vacuo and diethyl ether was added to the

M

+

C₅₀H₆₆¹¹B₂N₈O₂²³NaP₄S₄¹⁰²Ru₂: 1311.1313. Anal. Found: C, cannula filtration. The solid was redissolved in tetrahydrofuran

46.57; H, 5.28; N, 8.63%. Calcd for C₂₅H₃₃BN₄OP₂RuS₂: C, and layered with n-pentane. The filtrate was decanted to aﬀord

46.66; H, 5.17; N, 8.71%. Crystal data for C₂₅H₃₃BN₄OP₂RuS₂: a yellow precipitate that was dried in air. Yield: 0.042 g

M_w= 643.52, orthorhombic, Pbca, a = 8.5565(1), b = 18.5822(2), (0.055 mmol, 24%). Crystals suitable for crystallographic ana-

c = 36.1544(3) Å, V = 5748.50(5) Å³, Z = 8, D_calcd= 1.487 Mg lysis were obtained from vapour diﬀusion of n-pentane into a

m⁻³, μ(Cu Kα) = 7.03 mm⁻¹, T = 150(2) K, clear colourless concentrated solution of 16 in acetone over one day. IR (ATR,

block, 0.19 × 0.10 × 0.05 mm, 5806 independent reflections. F²cm⁻¹): 2354 ν_BH, 1905 ν_COcm⁻¹. IR (THF): 2338 ν_BH, 1923 ν_CO

.

refinement, R₁= 0.039, wR₂= 0.098 for 5659 reflections (I > ¹H NMR (700 MHz, CDCl₃): δ_H= 2.68 (s, 3 H, NCH₃), 3.55 (s, 3

2.0σ(I), 2θ_max= 144°), 328 parameters, 0 restraints, CCDC H, NCH₃), 6.15 (s, 1 H, NCHvCH), 6.51 (s, 1 H, NCHvCH),

1881123.†

6.66 (s, 1 H, NCHvCH), 6.73 (s, 1 H, NCHvCH), 6.97 (m.br., 3

H, C₆H₅), 7.04–7.07 (m, 2 H, C₆H₅), 7.22–7.24 (m, 1 H, C₆H₅),

7.28–7.47 (m, 9 H, C₆H₅), 7.71–7.79 (m, 3 H, C₆H₅), 7.90–7.92

Synthesis of [Ru(CO){P(OMe)₃}₂{BH(mt)₂}] (Ru→B)⁸(15)

A solution of [Ru(CO)(PPh₃)₂{BH(mt)₂}] (5: 0.202 g, 0.22 mmol) (m,

1 H, PCHvCHP), 7.97–7.99 (m, 1 H, PCHvCHP),

and P(OMe)₃(0.10 mL, 0.85 mmol) in tetrahydrofuran (20 mL) 8.04–8.06 (m, 2 H, C₆H₅). ¹³C{¹H} NMR (151 MHz, CDCl₃): δ_C=

was stirred for 18 h. The solvent was removed in vacuo and 33.3 (NCH₃), 34.3 (NCH₃), 120.4 (NCHvCH) overlapping with

4

diethyl ether (10 mL) and n-pentane (15 mL) were added to 120.5 (d, J_CP

=

3.0, NCHvCH), 120.8 (d, J_CP

=

3.0,

9.6,

9.4,

2,3

aﬀord a pale yellow solid that was isolated by cannula filtration NCHvCH), 121.7 (NCHvCH), 125.7 [d,

J

CP

and dried under high vacuum. Yield: 0.041 g (0.067 mmol, C^2,3,5,6(C₆H₅)], 127.4 [C⁴(C₆H₅)], 128.0 [d,

2,3

CP

30%). Crystals suitable for crystallographic analysis were C^2,3,5,6(C₆H₅)], 128.4 [d,

J

CP

= 8.8, C^2,3,5,6(C₆H₅)], 128.5 [d,

2,3

obtained from slow evaporation of a concentrated solution of

J

= 8.4, C^2,3,5,6(C₆H₅)], 128.7 [C⁴(C₆H₅)], 129.4 [C₄(C₆H₅)],

CP

15 in chloroform/n-pentane over one day. IR (ATR, cm⁻¹): 2358 129.6 [C⁴(C₆H₅)], 131.1 [d,

J

CP

= 8.5, C^2,3,5,6(C₆H₅)], 131.6 [d,

2,3

ν_BH, 1921 ν_CO. IR (THF, cm⁻¹): 2244 ν_BH, 1934 ν_CO

.

¹H NMR

J

CP

=

13.2, C^2,3,5,6(C₆H₅)], 133.0 [d,

J

=

14.6,

CP

(700 MHz, CDCl₃): δH = 3.49 (s, 3 H, NCH₃), 3.49 (s, 3 H, C^2,3,5,6(C₆H₅)], 133.4 [d,

J

CP

= 9.8, C^2,3,5,6(C₆H₅)], 135.5 [dd,

2,3

3

NCH₃), 3.56 (d, 9 H, J_HP= 10.8, OCH₃), 3.67 (d, 9 H, J_HP

=

¹J_CP= 44.1, J_CP= 4.5, C¹(C₆H₅)], 137.0 [d, ¹J_CP= 9.1, C¹(C₆H₅)],

11.1, OCH₃), 6.62 (d, 2 H, ⁴J_HP= 6.6, NCHvCH), 6.69 (dd, 2 H, 137.2 [d, ¹J_CP= 16.2, C¹(C₆H₅)], 139.5 [d, ¹J_CP= 27.2, C¹(C₆H₅)],

⁴J_HP= 8.1, J_HH= 1.8, NCHvCH). ¹³C{¹H} NMR (176 MHz, 148.1 [dd, ¹J_CP= 26.6, ²J_CP= 26.6, PCHvCHP], 149.0 (dd, ¹J_CP

=

3

2

3

CDCl₃): δ_C= 34.2 (NCH₃), 34.3 (NCH₃), 50.8 (br., P trans to B), 35.8, J_CP= 45.5, PCHvCHP), 164.5 (d, J_CP= 22.7, CS), 166.1

52.0 (d, ²J_CP= 5.9, P trans to S), 120.9 (d, ⁴J_CP= 4.2, NCHvCH), (d, ³J_CP= 19.6, ³J_CP= 1.5, CS), 206.9 (d, ²J_CP= 10.6, CO). ³¹P{¹H}

4

2

121.0 (d, J_CP

=

4.1, NCHvCH), 121.5 (d, J_CP

=

1.2, NMR (162 MHz, CDCl₃): δ_P= 70.6 (d, J_PP= 8.1, P trans to S),

NCHvCH), 121.6 (NCHvCH), 165.3 (d, J_CP= 24.3, CS), 166.9 50.8 (s.br., P trans to B). ¹¹B NMR (128 MHz, CDCl₃): δ_B= 5.05

3

(d, J_CP= 28.4, CS), 207.7 (dd, J_CP= 18.8, J_CP= 5.5, CO). (s.br.). ESI-MS(+) m/z: 765.1 [M + H]⁺. Accurate mass: Found

3

2

³¹P{¹H} NMR (162 MHz, CDCl₃): δ_P= 151.1 (d, J_PP= 19.4, P 765.0785 [M + H]⁺, Calcd for C₃₅H₃₄¹¹BN₄OP₂S₂¹⁰²Ru 765.0780.

2

trans to S), 153.7 (s.br., P trans to B). ³¹P NMR (162 MHz, Anal. Found: C, 54.97; H, 4.30; N, 7.22%. Calcd for

2

CDCl₃): δ_P= 151.1 (m, J_PP= 10.5, P trans to S), 153.7 (s.br., P C₃₅H₃₃BN₄OP₂RuS₂: C, 55.05; H, 4.36; N, 7.34%. Crystal data

trans to B). ¹¹B NMR (128 MHz, CDCl₃): δ_B= 3.62 (s.br.). ¹¹B for C₃₅H₃₃BN₄OP₂RuS₂: M_w= 763.63, triclinic, P1 (no. 2), a =

ˉ

{¹H} NMR (128 MHz, CDCl₃): δ_B= 3.80 (s.br.). ESI-MS(+) m/z: 10.4568(5), b = 12.4325(5), c = 15.9030(7) Å, α = 68.191(4)°, β =

617.0 [M + H]⁺. Accurate mass: Found 617.0166 [M + H]⁺, 82.434(4)°, γ = 71.916(4)°, V = 1824.35(8) Å³, Z = 2, D_calcd

=

Calcd for C₁₅H₂₉¹¹BN₄O₇P₂S₂¹⁰²Ru: 617.0162. Anal. Found: 1.390 Mg m⁻³, μ(Cu Kα) = 5.64 mm⁻¹, T = 150(2) K, yellow

C, 29.35; H, 4.71; N, 8.98%. Calcd for C₁₅H₂₉BN₄O₇P₂RuS₂: block, 0.21 × 0.14 × 0.07 mm, 7333 independent reflections. F²

C, 29.28; H, 4.75; N, 9.10%. Crystal data for refinement, R₁= 0.037, wR₂= 0.101 for 6926 reflections (I >

ˉ

(C₁₅H₂₉BN₄O₇P₂RuS₂)₃: M_w= 1846.13, triclinic, P1 (no. 2), a = 2.0σ(I), 2θ_max= 144°), 418 parameters, 0 restraints, CCDC

9.4439(1), b = 15.2581(3), c = 26.4419(4) Å, α = 93.1670(14)°, β = 1881125.†

Dalton Trans.

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Dalton Transactions

Paper

Attempted synthesis of [Ru{κ³-B,S,S′-B(mt)₂}(CO)(PPh₃)₂]PF₆;

observation of [RuF(Hmt)₂(CO)(PPh₃)₂]PF₆[11]PF₆

5 Herein we consider the borane cage in metallaboratranes

to be neutral BR₃units such that complexes such as 1 are

deemed to be zerovalent. For further discussions on oxi-

dation state and dⁿassignments for metallaboratranes see:

(a) A. F. Hill, Organometallics, 2006, 25, 4741–4743;

(b) G. Parkin, Organometallics, 2006, 25, 4744–4747.

A

solution of [Ru(CO)(PPh₃)₂{BH(mt)₂}] (5: 0.100 g,

0.112 mmol) and [CPh₃]PF₆(0.037 g, 0.095 mmol) in tetra-

hydrofuran (10 mL) was stirred for 24 h. The solvent was

removed in vacuo and diethyl ether (10 mL) was added to

aﬀord an orange precipitate that was isolated via cannula fil-

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A. J. P. White and D. J. Williams, Chem. Commun., 2005,

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A. C. Willis, Organometallics, 2005, 24, 4083–4086;

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L. N. Zakharov, G. P. A. Yap, C. D. Incarvito,

A. L. Rhenigold and D. Rabinovich, Dalton Trans., 2004,

1626–1634; (f) H. Zhu, Q. Ma, A.-Q. Jia, Q. Chen,

W.-H. Leung and Q.-F. Zhang, Inorg. Chim. Acta, 2013, 405,

427–436; (g) R. J. Blagg, J. P. H. Charmant, N. G. Connelly,

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5221–5230; ( j) R. J. Blagg, N. G. Connelly, M. F. Haddow,

A. Hamilton, M. Lusi, A. G. Orpen and B. M. Ridgeway,

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H. Othman and G. R. Owen, Organometallics, 2012, 31,

6753–6760; (o) S. Holler, M. Tüchler, A. M. Knaus, F. Belaj

and N. C. Mösch-Zanetti, Polyhedron, 2017, 125, 122–129;

(p) G. Nuss, G. Saischek, B. N. Harum, M. Volpe,

K. Gatterer, F. Belaj and N. C. Mösch-Zanetti, Inorg. Chem.,

2011, 50, 1991–2001; (q) S. Holler, M. Tüchler, F. Belaj,

L. F. Veiros, K. Kirchner and N. Mösch-Zanetti, Inorg.

Chem., 2016, 55, 4980–4991; (r) S. Holler, M. Tüchler,

M. C. Roschger, F. Belaj, L. F. Veiros, K. Kirchner and

N. C. Mösch-Zanetti, Inorg. Chem., 2017, 56, 12670–12673;

(s) G. Nuss, G. Saischek, B. N. Harum, M. Volpe, F. Belaj

and N. C. Mösch-Zanetti, Inorg. Chem., 2011, 50, 12632–

12640; (t) S. Senda, Y. Ohki, T. Hirayama, D. Toda,

J.-L. Chen, T. Matsumoto, H. Kawaguchi and K. Tatsumi,

Inorg. Chem., 2006, 24, 9914–9925.

tration. Crude mixture: IR (THF, cm⁻¹): 1931 ν_CO, 1972 ν_CO

.

³¹P

1

{¹H} NMR (162 MHz, C₆D₆): δ_P= 39.6 (s.br.), −142.9 (h, J_PF

=

713.9, PF₆), −5.3 (s.br., PPh₃). The orange precipitate had poor

solubility in C₆D₆. ³¹P{¹H} NMR (162 MHz, CDCl₃): δ_P= 43.8,

1

39.0 (s.br.), 35.3, 26.2, 24.9, −144.3 (h, J_PF= 714.7, PF₆), −5.3

(PPh₃). Crystals of [RuF(Hmt)₂(CO)(PPh₃)₂]PF₆[11]PF₆suitable

for crystallographic analysis were obtained from slow evapor-

ation of a concentrated solution of the crude reaction mixture

in benzene/n-pentane over one day. Crystal data for

C₄₅H₄₂FN₄OP₂RuS₂·F₆P·C₆H₆: M_w= 1124.03, monoclinic, P2₁/c,

a = 14.5664(1), b = 15.1058(1), c = 23.6542(2) Å, V = 5016.47(7)

Å³, Z = 4, D_calcd= 1.488 Mg m⁻³, μ(Cu Kα) = 4.80 mm⁻¹, T =

150(2) K, yellow block, 0.18 × 0.11 × 0.07 mm, 10 144 indepen-

dent reflections. F²refinement, R₁= 0.044, wR₂= 0.104 for

9278 reflections (I > 2.0σ(I), 2θ_max= 144°), 729 parameters, 96

restraints, CCDC 1881121.†

Conﬂicts of interest

The authors declare no conflicts of interest.

Acknowledgements

This work was supported by the Australian Research Council

(DP170102695).

Notes and references

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Methimazolyl based diptych bicyclo-[3.3.0]-ruthenaboratranes

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