Certainly! Here’s a **step-by-step, quantitative, database-style classification** of your phosphine ligands, with explanation and summarization of the relevant **physicochemical properties**:

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## 1. **Identify & Summarize Quantitative Physicochemical Properties**

For tertiary phosphine ligands, the following quantitative properties are often key:

- **Steric Bulk:**  
  - Measured quantitatively as either the **cone angle (θ, in degrees)** or **percent buried volume (%V<sub>bur</sub>)**.
- **Electronic Effects:**  
  - Measured as the **Tolman Electronic Parameter (TEP, in cm<sup>−1</sup>)**—lower values indicate more electron-donating.
- **Solubility/Polarity:**  
  - Can be approximated quantitatively via **logP (octanol/water partition coefficient)** or **dielectric constant**.
- **Hydrogen-bonding ability:**  
  - Quantified by the number of H-bond donors/acceptors (from SMILES/structure).

### For this analysis, I’ll focus on these two primary, database-quantifiable properties—**Steric Bulk (cone angle or % buried volume)** and **Electronic Donor Strength (using Tolman Parameter or Hammett constants, if applicable)**.

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## 2. **Compile Quantitative Features for Each Ligand**

Let's estimate or cite typical data for related substituents:

| Ligand SMILES | Phosphine Substituents | Expected Main Steric Bulk (Cone Angle/°)/%V<sub>bur</sub> | Main Electronic Descriptor (TEP/cm<sup>−1</sup>) |
| ------------- | --------------------- | -------------------------------------------------------- | ----------------------------------------------- |
| ditert-butyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane | t-Bu<sub>2</sub>, 2-[2,4,6-tri(iPr)<sub>3</sub>C<sub>6</sub>H<sub>2</sub>]-Ph | t-Bu<sub>2</sub>P- ≈160-175°, large; Ar-sub, very bulky | t-Bu<sub>2</sub>PR: TEP ≈ 2056–2058 |
| ditert-butyl-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane | t-Bu<sub>2</sub>, Ar(OMe)<sub>2</sub> | Slightly larger than above, OMe increases electron-donating | OMe more donating, TEP ≈ 2054–2056 |
| dicyclohexyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane | Cy<sub>2</sub>, Ar-sub | Cy<sub>2</sub>P- ≈ 170–180°, slightly less bulky than t-Bu<sub>2</sub> | Cy<sub>2</sub>P: TEP ≈ 2054–2056 |
| bis(1-adamantyl)-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane | Ad<sub>2</sub>, Ar(OMe)<sub>2</sub> | Ad<sub>2</sub>P- ≈ 180–185°, very bulky | Ad derivatives: TEP ≈ 2052–2055 |

> **Data notes:**  
> - **Tolman cone angles and TEPs** for t-Bu<sub>2</sub>P-, Cy<sub>2</sub>P-, and Ad<sub>2</sub>P- are well-established (see N. Tolman, Chem. Rev. 1977). The functionalized aryl groups further increase both steric bulk and electron-donating ability.

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## 3. **Define Cutoffs for Grouping (Based on Quantitative Data)**

### - **Steric Bulk**
  - **Medium:** Cone angle ≤170°, %bur <48%
  - **Bulky:** 170° < cone angle ≤180°, %bur ~48–54%
  - **Superbulky:** Cone angle >180°, %bur >54%
  
### - **Electronic Parameter (Strongly electron-donating if TEP < 2055 cm⁻¹)**

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## 4. **Classify Ligands Based on Quantitative Data**

| Ligand                                             | Steric Group         | Electronic Group      |
|--------------------------------------------------- |----------------------|----------------------|
| ditert-butyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane           | Bulky (θ ≈ 170-175°) | Strong donor (TEP ≈ 2056)   |
| ditert-butyl-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane | Bulky (θ ≈ 170-175°) | Very strong donor (TEP ≈ 2055) |
| dicyclohexyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane              | Bulky (θ ≈ 175-180°) | Very strong donor (TEP ≈ 2054) |
| bis(1-adamantyl)-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane | Superbulky (θ ≈ 185°) | Extremely strong donor (TEP ≈ 2052–2054) |

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## 5. **Final Classification (MAX = 3 GROUPS)**

### **Option A:** **:o:By Steric Bulk Only:o: (most database-like relevant property for these phosphines)**

- **Bulky Phosphines (cone angle 170–180°):**
  - ditert-butyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane
  - ditert-butyl-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane
  - dicyclohexyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane

- **Superbulky Phosphines (cone angle >180°):**
  - bis(1-adamantyl)-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane

### **Option B:** **If grouped :o:by Electron Donor Strength:o: (all are strong due to aromatic/alkyl/OMe substituents, TEP 2052–2056)**
- **All classified in a single group** as “Strong σ-donor phosphines (TEP 2052–2056 cm⁻¹)”.

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## 6. **Summary Table**

| Group    | Criteria                                    | Members                                                                                                                                                         |
|----------|---------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Bulky    | Cone angle 170–180° (%bur 48–54%)           | ditert-butyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane; ditert-butyl-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane; dicyclohexyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane |
| Superbulky | Cone angle >180° (%bur >54%)                | bis(1-adamantyl)-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane                                                                                 |

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## 7. **Justification & Comments**

- **Steric bulk is the primary quantifiable classifier:** Cone angle and percent buried volume are standard, database-quantitative measures for phosphines. Electronic donor strength (TEP) is high and similar for all, so not a useful discriminator.
- **If one class is preferred:** All would be considered **“Bulky, strong-donor, trialkylaryl phosphines,”** as they all exceed classic “standard-bulky” markers (e.g., PPh<sub>3</sub>, PCy<sub>3</sub>).

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# **Final Classification**

**:o:PRIMARY, PHYSICOCHEMICALLY-JUSTIFIED GROUPING (BASED ON STERIC BULK)::o:**

1. **Bulky (cone angle 170–180°):**
    - ditert-butyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane
    - ditert-butyl-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane
    - dicyclohexyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane

2. **Superbulky (cone angle >180°):**
    - bis(1-adamantyl)-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane

**SECONDARY, ELECTRONIC:**  
All can be *grouped together* as “very strong electron donors (TEP 2052–2056 cm⁻¹)”—quantitative difference is small.

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**If only one class is allowed by the strictest reading:**  
**All four substances may be merged into a single class of “Bulky, strongly electron-donating trialkylaryl phosphines (cone angle >170°, TEP 2052–2056 cm⁻¹)”**, as the discriminating quantitative values are tightly clustered.

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### **References to Quantitative Data:**
- Tolman, C. A. Chem. Rev. 1977, 77, 313–348. (cone angles, TEP)
- Cavallo, L.; Nolan, S. P. et al. Chem. Rev. 2016, 116, 9, 8173–8306. (% buried volume)

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## **In summary:**

- **Preferred (max 2 classes, database-aligned):**  
  - **Bulky:** First three ligands  
  - **Superbulky:** bis(1-adamantyl)-...

- **Alternatively (if allowed/justified):**  
  All in one class: “Bulky, strongly electron-donating tertiary phosphines.”  
  (Strongest justification: quantitative data for sterics/electronics is tightly clustered.)