Compound characterization data — Kulyabin et al., 2026

Pavel S. Kulyabin, Alejandra Sophia Lozano Perez, David B. Cordes, Aidan P. Mackay, Amit Kumar. “Ligand backbone engineering enables pincer catalysts for highly efficient hydrogenation reactions.” ChemRxiv (2026). https://doi.org/10.26434/chemrxiv.15007666/v1

cis-(piperidine-2,6-diyl)dimethanol
Identifier	P2
¹H NMR (400 MHz, CD₃OD, 298 K)	δ 3.54 (dd, J = 10.7, 4.1 Hz, 2H), 3.38 (dd, J = 10.7, 8.5 Hz, 2H), 2.66 (ddq, J = 11.2, 6.5, 2.4 Hz, 2H), 1.93 – 1.76 (m, 1H), 1.69 – 1.53 (m, 2H), 1.42 (qt, J = 13.2, 4.0 Hz, 1H), 1.04 (qd, J = 12.9, 4.0 Hz, 2H)
¹³C NMR {¹H} (101 MHz, CD₃OD, 298 K)	δ, 67.1, 59.4, 29.1, 24.9
HRMS (ESI)	calcd for C₇H₁₅NNaO₂⁺ [M+Na]⁺: 168.0995, found: 168.0994

cis-2,6-bis(chloromethyl)piperidine
Identifier	P3
¹H NMR (400 MHz, CDCl₃, 298 K)	δ 3.56 (dd, J = 10.7, 3.8 Hz, 2H), 3.41 (dd, J = 10.7, 8.7 Hz, 2H), 2.81 (dddd, J = 11.2, 8.7, 3.7, 2.5 Hz, 2H), 2.53 (br.s, 1H), 1.87 (m, 1H), 1.67 (m, 2H), 1.39 (qt, J = 13.2, 3.9 Hz, 1H), 1.10 (tdd, J = 13.0, 11.5, 4.0 Hz, 2H)
¹³C NMR {¹H} (101 MHz, CDCl₃, 298 K)	δ 57.5, 49.8, 30.1, 23.9
HRMS (ESI)	calcd for C₇H₁₄Cl₂N⁺ [M+H]⁺: 182.0498, found: 182.0498

cis-2,6-bis((ethylthio)methyl)piperidine
Identifier	L1
¹H NMR (400 MHz, CD₃OD, 298 K)	δ, 2.75 (dd, J = 13.4, 4.0 Hz, 2H), 2.62 (m, 2H), 2.56 (qd, J = 7.4, 1.8 Hz, 6H), 2.39 (dd, J = 13.4, 9.7 Hz, 2H), 1.88 – 1.77 (m, 1H), 1.77 – 1.67 (m, 2H), 1.42 (qt, J = 13.1, 3.9 Hz, 1H), 1.26 (s, 6H), 1.08 (tdd, J = 13.1, 11.3, 4.0 Hz, 2H)
¹³C NMR {¹H} (101 MHz, CD₃OD, 298 K)	δ 56.6, 39.0, 33.0, 26.7, 25.5, 15.4
HRMS (ESI)	calcd for C₁₁H₂₄NS₂⁺ [M+H]⁺: 234.1345, found: 234.1345

dimethyl 4-hydroxypyridine-2,6-dicarboxylate hydrochloride
¹H NMR (400 MHz, CD₃OD, 298 K)	δ, 7.87 (s, 2H), 4.09 (s, 6H)
¹³C NMR {¹H} (101 MHz, CD₃OD, 298 K)	δ, 174.7, 161.5, 145.5, 117.7, 54.8

methyl 4-methoxypyridine-2,6-dicarboxylate hydrochloride
Identifier	P4
Name in characterization text	Dimethyl 4-methoxypyridine-2,6-dicarboxylate
¹H NMR (400 MHz, CDCl₃)	δ 7.81 (s, 2H), 4.00 (s, 6H), 3.97 (s, 3H)

dimethyl (2R,4s,6S)-4-methoxypiperidine-2,6-dicarboxylate
Identifier	P5
¹H NMR (400 MHz, CDCl₃, 298 K)	δ, 3.74 (s, 6H), 3.40 – 3.34 (m, 2H), 3.36 (s, 3H), 3.34 – 3.24 (m, 1H), 2.38 (m, 2H), 2.31 (m, 1H), 1.27 (q, J = 12.1 Hz, 2H)
¹³C NMR {¹H} (101 MHz, CDCl₃, 298 K)	δ 172.2, 77.1, 56.6, 55.8, 52.4, 34.7
HRMS (ESI)	calcd for C₁₀H₁₇NNaO₅⁺ [M+Na]⁺: 254.0999, found: 254.0994

((2R,4s,6S)-4-methoxypiperidine-2,6-diyl)dimethanol
Identifier	P6
¹H NMR (400 MHz, CD₃OD, 298 K)	δ 3.56 (dd, J = 10.8, 4.2 Hz, 2H), 3.44 (dd, J = 10.7, 8.0 Hz, 2H), 3.37 – 3.32 (m, 1H), 3.35 (s, 3H), 2.70 (dddt, J = 11.9, 6.5, 4.1, 2.2 Hz, 2H), 2.12 – 1.93 (m, 2H), 0.93 (q, J = 11.8 Hz, 2H)
¹³C NMR {¹H} (101 MHz, MeOD, 298 K)	δ, 78.8, 66.7, 57.5, 55.8, 35.2
HRMS (ESI)	calcd for C₈H₁₇NNaO₃⁺ [M+Na]⁺: 198.1101, found: 198.1098

(2R,4s,6S)-2,6-bis(chloromethyl)-4-methoxypiperidine
Identifier	P7
¹H NMR (400 MHz, CD₃OD, 298 K)	δ, 3.67 (dd, J = 10.9, 4.2 Hz, 2H), 3.52 (dd, J = 10.9, 7.8 Hz, 2H), 3.37 – 3.32 (m, 1H), 3.36 (s, 3H), 2.89 (dddd, J = 11.8, 7.8, 4.2, 2.4 Hz, 2H), 2.20 – 2.08 (m, 2H), 1.00 (q, J = 11.6 Hz, 2H)
¹³C NMR {¹H} (101 MHz, CD₃OD, 298 K)	δ, 78.1, 56.6, 56.0, 49.5, 36.3
HRMS (ESI)	calcd for C₈H₁₅Cl₂NNaO⁺ [M+Na]⁺: 234.0423, found: 234.0420

(2R,4s,6S)-2,6-bis((ethylthio)methyl)-4-methoxypiperidine
Identifier	L2
¹H NMR (400 MHz, CDCl₃, 298 K)	δ, 3.35 (s, 3H), 3.22 (tt, J = 11.0, 4.4 Hz, 1H), 2.71 (dd, J = 12.6, 4.1 Hz, 2H), 2.68 – 2.60 (m, 3H), 2.56 (q, J = 7.4 Hz, 4H), 2.50 (dd, J = 12.6, 8.5 Hz, 2H), 2.09 (dd, J = 11.7, 4.2 Hz, 2H), 1.26 (t, J = 7.4 Hz, 7H), 1.05 (q, J = 11.1 Hz, 2H)
¹³C NMR {¹H} (101 MHz, CDCl₃, 298 K)	δ, 77.8, 55.8, 53.8, 38.7, 38.2, 26.6, 15.1
HRMS (ESI)	calcd for C₁₂H₂₅NNaOS₂⁺ [M+Na]⁺: 286.1270, found: 286.1266

Ru-4
NMR sample	Mixture of 3 isomers differing by the relative orientation of the SEt groups with respect to the SNS ligand plane
¹H NMR (400 MHz, CD₂Cl₂, 298 K)	δ, 7.68 – 7.52 (m, 6H), 7. 33 (m, 9H), [4.29 (m), 4.09 (br.s), 3.73 (br.s), 3.52 (br.s), 2H], 3.38 (q, J = 11.9 Hz, 1H), 3.24 (dd, J = 11.1, 2.5 Hz, 1H), 2.72 (m, 2H), 2.66 (m, 1H), 2.34 (t, J = 12.0 Hz, 1H), 2.11 (m, 1H), 2.04 (m, 1H), 2.01 – 1.90 (m, 1H), [1.64 (m), 1.78 – 1.50 (m), 3H), 1.49 – 1.24 (m, 3H), [1.00 (t, J = 7.5 Hz), 0.91 (t, J = 6.7 Hz), 6H)
¹³C NMR {¹H} (101 MHz, CD₂Cl₂, 298 K)	δ, 137.3 (d, J = 38.8 Hz), 134.7 (d, J = 10.0 Hz), 129.2 (d, J = 9.4 Hz), 127.7 (d, J = 9.1 Hz), 127.6, 57.6, 55.9, 46.0, 43.1, 42.6, 30.9, 30.5, 29.5, 27.3, 26.5, 23.1, 22.7, 13.0, 12.9
³¹P NMR {¹H} (162 MHz, CD₂Cl₂, 298 K)	δ, 49.96, 48.27, 46.93
HRMS (ESI)	calcd for C₂₉H₃₈ClNPRuS₂⁺ [M − Cl]⁺: 632.0910, found: 632.0910

Ru-4-H
NMR sample	Mixture of 3 isomers differing by the relative orientation of the SEt groups with respect to the SNS ligand plane
¹H NMR (500 MHz, C₆D₆, 298 K)	δ, 7.62 (m, 6H), 7.13 (t, J = 6.7 Hz, 6H), 7.04 (t, J = 7.0 Hz, 3H), [3.43 (m), 3.20 (br.s), 2H], 2.71 (m, 2H), 2.49 – 2.21 (m, 4H), 2.13 – 1.66 (m, 4H), 1.44 (br.s, 2H), 1.17 – 0.57 (m, 8H), [−22.00 (br.s), −22.86 (br.s), −24.25 (d, J = 48.4 Hz) 1H]
¹³C NMR {¹H} (126 MHz, C₆D₆, 298 K)	δ, 142.4 (d, J = 32.9 Hz), 134.3 (d, J = 11.8 Hz), 127.6 (d, J = 7.1 Hz), 63.2, 48.5, 34.1, 33.1, 24.2, 14.1
³¹P NMR {¹H} (202 MHz, C₆D₆, 298 K)	δ, 69.00, 68.14
HRMS (ESI)	calcd for C₂₉H₃₉NPRuS₂⁺ [M + H]⁺: 598.1300, found: 598.1309

Ru-5
¹H NMR (500 MHz, CD₂Cl₂, 298 K)	δ, [7.66 (m), 7.58 (m), 7.53 (m), 6H], 7.33 (m, 9H), [4.30 (m), 4.13 (br.s), 3.80 (m), 3.58 (br.s), 2H], 3.55 – 3.38 (m, 2H), 3.36 (s, 3H), 3.24 (m, 1H), 2.74 (m, 3H), 2.56 –2.29 (m, 4H), [1.73 (br.s), 1.55 (m), 1.41 (dq, J = 14.7, 7.3 Hz) 1.37 – 1.17 (m), 4H], [1.01 (t, J = 7.3 Hz), 0.91 (m), 6H]
¹³C NMR {¹H} (126 MHz, CD₂Cl₂, 298 K)	δ, 137.2 (d, J = 40.3 Hz, minor), 137.1 (d, J = 39.2 Hz, major), 134.7 (d, J = 9.5 Hz, minor), 134.6 (d, J = 9.9 Hz, major), 129.3 (major), 129.26(minor), 127.8 (d, J = 9.0 Hz), 127.6 (d, J = 8.9 Hz), 75.8(major), 75.7(minor), 56.1(minor), 56.0(major), 54.8(minor), 45.4(major), 42.5(minor), 36.6(major), 36.3 (minor), 29.5(major), 27.3 (minor), 13.0 (major), 12.8 (minor)
³¹P NMR {¹H} (202 MHz, CD₂Cl₂, 298 K)	δ, 49.90, 48.28, 46.87
HRMS (ESI)	calcd for C₃₀H₄₀ClNOPRuS₂⁺ [M − Cl]⁺: 662.1016, found: 662.1013

Ru-5-H
¹H NMR (500 MHz, C₆D₆, 298 K)	δ, 7.91 (m, 6H), 7.13 (m, 6H), 7.04 (m, 3H), 3.43 (br.s, 2H), 3.26 (s, 3H), 3.25 – 3.07 (m, 1H), 2.67 (br.s, 2H), 2.56 – 2.14 (m, 6H), 2.14 – 1.67 (m, 2H), 1.23 – 0.53 (m, 8H), [−22.22, −23.17, −24.50, 1H]
¹³C NMR {¹H} (126 MHz, C₆D₆, 298 K)	δ, 142.3, 142.1, 134.4, 134.2, 127.7, 127.6, 78.0, 62.0, 55.0, 47.8, 38.9, 33.9, 14.0
³¹P NMR {¹H} (202 MHz, C₆D₆, 298 K)	δ, 69.12 (br.s), 68.18(br.s)

Ru-4-H₂
NMR observation (5 bar H₂)	The presented NMR analysis, taken immediately after, demonstrated formation of ruthenium dihydrides
¹H NMR (500 MHz, C₆D₆, 298 K)	δ, [8.38 (m, minor), 8.09 (m, major), 8.00 (m, minor), 7.94 (m, minor), 6H], 7.23 (m, 6H), 7.10 (m, 3H), 6.88 (m, 1H), 3.06 (m, 2H), 2.90 (t, J = 12.7 Hz, 2H), 2.57 (d, J = 12.4 Hz, 2H), 2.19 (dq, J = 14.1, 7.0 Hz, 2H), 1.95 (dq, J = 14.5, 7.1 Hz, 2H), 1.52 (m, 2H), 1.30 (m, 2H), 1.29–1.13 (m, 2H), [0.89 (m, minor), 0.75 (t, J = 7.3 Hz, major), 6H], [−6.12 (br.s, minor), −6.75 (d, J = 18.0 Hz, major), 1H], [−6.80 (br.s, minor), −7.14 (d, J = 17.2 Hz, major), 1H]. ]
¹³C NMR {¹H} (126 MHz, C₆D₆, 298 K)	δ, 143.4 (d, J = 32.6 Hz), 134.6 (d, J = 11.0 Hz), 128.3, 127.4 (d, J = 8.2 Hz), 61.4, 44.7, 44.0, 28.8, 23.8, 14.0
³¹P NMR {¹H} (202 MHz, C₆D₆, 298 K)	δ, 82.86 (minor), 76.93 (major)

Ru-5-H₂
NMR observation (5 bar H₂)	NMR analysis demonstrated formation of ruthenium dihydrides
¹H NMR (500 MHz, C₆D₆, 298 K)	δ, [8.37 (br.s, minor), 8.15 (t, J = 8.3 Hz, major), 7.90 (m, minor), 6H], 7.26 (t, J = 7.4 Hz, 6H), 7.11 (t, J = 7.2 Hz, 3H), 6.59 (m, 1H), [3.25 (m, minor), 3.07 (m), 1H], 3.04 (s, 3H), 2.95 (m, 4H), 2.47 (q, J = 10.1 Hz, 2H), 2.17 (dq, J = 14.2, 7.1 Hz, 2H), 1.98 (dq, J = 14.7, 7.4 Hz, 2H), 1.68 (m, 2H), 1.46 (m, 2H), [0.89 (m, minor), 0.77 (t, J = 7.3 Hz), 6H], [−6.19 (br.s, minor) −6.78 (d, J = 18.1 Hz, major), 1H], [−6.79 (br.s, minor), −7.12 (d, J = 16.8 Hz, major), 1H]
¹³C NMR {¹H} (126 MHz, C₆D₆, 298 K)	δ, 143.2 (d, J = 33.3 Hz), 134.8 (d, J = 11.0 Hz), 128.3, 127.4 (d, J = 8.3 Hz), 77.0, 59.8, 55.1, 44.2, 44.2, 34.9, 14.0
³¹P NMR {¹H} (202 MHz, C₆D₆, 298 K)	δ, 82.82 (minor), 76.46 (major)

Ru-4-EtOH
NMR observation	NMR analysis demonstrated formation of new ruthenium hydride which was assigned as Ru-4-EtOH
¹H NMR (400 MHz, toluene-d₈)	δ, 7.91 (br.s, 6H), 7.16 (m, 6H), 7.09 (m, 3H), 3.43 (q, J = 6.8 Hz, 2H, EtOH), 3.32–2.91 (m, 2H), 2.90–2.49 (m, 3H), 2.48–2.08 (m, 7H), [1.84 (m), 1.44 (m), 5H], 1.04 (t, J = 6.8 Hz, 3H, EtOH), [0.80 (m), 0.69 (m), 6H], [−20.55 (br.s), −20.79 (br.s), 1H]
³¹P NMR {¹H} (162 MHz, toluene-d₈)	δ, 67.49, 66.54, 66.40

Ru-3 and Ru-4 with KOtBu and EtOH
NMR sample	Ru-3 or Ru-4 (0.015 mmol), KOtBu (0.03 mmol), EtOH (11 mmol), and toluene-d₈
NMR monitoring duration	120 °C: 18 h; 150 °C: 21.5 h
NMR observation (120 °C, 30 min)	Formation of ethoxides mer-Ru-4-EtOH and mer-Ru-3-EtOH was observed
NMR observation (150 °C)	While for Ru-4 signals assigned to ruthenium hydrides persisted even at 150 °C, they completely disappeared in the case of Ru-3

Ru-4, Ru-5, Ru-4-H, and Ru-5-H
Single-crystal X-ray diffraction, structural assignment	Single-crystal X-ray diffraction analysis confirmed both the syn configuration of the piperidine backbone and the meridional coordination geometry at ruthenium for all four complexes
Single-crystal X-ray diffraction, Ru-4 formula	C₂₉H₃₈Cl₂NPRuS₂
Single-crystal X-ray diffraction, Ru-5 formula	C₃₀H₄₀Cl₂NOPRuS₂
Single-crystal X-ray diffraction, Ru-4-H formula	C₃₂H₄₅NPRuS₂
Single-crystal X-ray diffraction, Ru-5-H formula	C₃₀H₄₀NOPRuS₂
Single-crystal X-ray diffraction, formula weight	Ru-4: 667.66; Ru-5: 697.69; Ru-4-H: 639.85; Ru-5-H: 626.79
Single-crystal X-ray diffraction, crystal size (mm³)	Ru-4: 0.16×0.10×0.01; Ru-5: 0.22×0.13×0.08; Ru-4-H: 0.25×0.13×0.09; Ru-5-H: 0.05×0.03×0.02
Single-crystal X-ray diffraction, temperature (K)	Ru-4: 100; Ru-5: 100; Ru-4-H: 173; Ru-5-H: 100
Single-crystal X-ray diffraction, space group	Ru-4: P2₁/c; Ru-5: P2₁/n; Ru-4-H: P1̅; Ru-5-H: P2₁/c
Single-crystal X-ray diffraction, a (Å)	Ru-4: 10.4418(2); Ru-5: 10.50210(10); Ru-4-H: 10.02624(14); Ru-5-H: 11.2496(3)
Single-crystal X-ray diffraction, b (Å)	Ru-4: 11.1881(3); Ru-5: 9.98430(10); Ru-4-H: 13.25359(19); Ru-5-H: 9.8687(3)
Single-crystal X-ray diffraction, c (Å)	Ru-4: 25.2437(6); Ru-5: 29.4459(4); Ru-4-H: 13.95827(17); Ru-5-H: 26.4690(7)
Single-crystal X-ray diffraction, α (°)	Ru-4-H: 64.4848(13)
Single-crystal X-ray diffraction, β (°)	Ru-4: 92.325(2); Ru-5: 92.0490(10); Ru-4-H: 75.5067(11); Ru-5-H: 100.036(2)
Single-crystal X-ray diffraction, γ (°)	Ru-4-H: 69.8446(13)
Single-crystal X-ray diffraction, volume (Å³)	Ru-4: 2946.64(12); Ru-5: 3085.61(6); Ru-4-H: 1560.02(4); Ru-5-H: 2893.60(14)
Single-crystal X-ray diffraction, Z	Ru-4: 4; Ru-5: 4; Ru-4-H: 2; Ru-5-H: 4
Single-crystal X-ray diffraction, ρ (calc) (g/cm³)	Ru-4: 1.505; Ru-5: 1.502; Ru-4-H: 1.362; Ru-5-H: 1.439
Single-crystal X-ray diffraction, μ (mm⁻¹)	Ru-4: 0.929; Ru-5: 0.893; Ru-4-H: 0.709; Ru-5-H: 0.765
Single-crystal X-ray diffraction, F(000)	Ru-4: 1376; Ru-5: 1440; Ru-4-H: 670; Ru-5-H: 1304
Single-crystal X-ray diffraction, reflections collected	Ru-4: 65622; Ru-5: 68008; Ru-4-H: 34373; Ru-5-H: 60114
Single-crystal X-ray diffraction, independent reflections (Rᵢₙₜ)	Ru-4: 7825 (0.0652); Ru-5: 8454 (0.0390); Ru-4-H: 7430 (0.0259); Ru-5-H: 7018 (0.0637)
Single-crystal X-ray diffraction, parameters, restraints	Ru-4: 425, 25; Ru-5: 350, 1; Ru-4-H: 423, 128; Ru-5-H: 332, 1
Single-crystal X-ray diffraction, GoF on F²	Ru-4: 1.100; Ru-5: 1.037; Ru-4-H: 1.043; Ru-5-H: 1.011
Single-crystal X-ray diffraction, R₁ [I > 2σ(I)]	Ru-4: 0.0384; Ru-5: 0.0218; Ru-4-H: 0.0226; Ru-5-H: 0.0333
Single-crystal X-ray diffraction, wR₂ (all data)	Ru-4: 0.0860; Ru-5: 0.0500; Ru-4-H: 0.0550; Ru-5-H: 0.0678
Single-crystal X-ray diffraction, largest difference peak/hole (e/Å³)	Ru-4: 0.882/−0.732; Ru-5: 0.435/−0.540; Ru-4-H: 0.420/−0.297; Ru-5-H: 0.535/−0.562
Single-crystal X-ray diffraction, Ru-4 disorder	In Ru-4 about half of the L1 ligand and both the chlorides were disordered over two sites resulting from the formation of a nearly equal-part mixture of complexes with L1 adopting cis/trans arrangements of the thioether arms. The terminal methyl on the other half of L1 was also disordered
Single-crystal X-ray diffraction, Ru-4-H disorder	In a similar manner in Ru-4 about half of the L1 ligand in Ru-4-H were disordered over two sites resulting from the formation of a small proportion (~15 %) of complexes with L1 adopting trans arrangements of the thioether arms. The hexane solvate was also disordered over two sites

BDM obtained via PET hydrogenation using Ru-5
Residual ruthenium analysis (4210 MP-AES; the source also identifies the method as ICP-MS), sample	100 mg BDM dissolved in 10 mL of a 3 % HNO₃ solution in water
Residual ruthenium analysis, Main summary	0.4 ppm
Residual ruthenium analysis, SI summary	0.3-0.4 ppm
Residual ruthenium analysis, Ru (349.894 nm), replicates 1–3 (ppm)	0.41330708, 0.41770905, 0.40430529
Residual ruthenium analysis, Ru (372.693 nm), replicates 1–3 (ppm)	0.40324382, 0.40743294, 0.40637054
Residual ruthenium analysis, Ru (372.803 nm), replicates 1–3 (ppm)	0.39399378, 0.38434434, 0.38629267
Residual ruthenium analysis, Ru (379.935 nm), replicates 1–3 (ppm)	0.27823487, 0.29499592, 0.31806801